How do Continuationists explain the fact that the vast majority of Christians have never personally experienced "overtly miraculous" spiritual gifts?

Consider what happened during biblical times when there were overt miracles:

He divided the sea and caused them to pass through;
And He made the waters stand up like a heap.
In the daytime also He led them with the cloud,
And all the night with a light of fire.
He split the rocks in the wilderness,
And gave them drink in abundance like the depths.
He also brought streams out of the rock,
And caused waters to run down like rivers.

But they sinned even more against Him …
— Psalm 78:13–17

Time and again, God or his prophets demonstrated spectacular miracles to people that already believed, and in almost all cases, those people were awed, but only briefly, before returning to their sinful ways.

Spectacular miracles get people’s attention, but they don’t have lasting effects.

Jesus used overt miracles both to attract and retain a small number of loyal followers and to leave an impression on other people so that they would remember what had happened after he was gone. But very few people were convinced simply by having seen these events.

Since then the church of God itself has remained small; this is not the time when God is trying to convert and save the world (if it is, he’s been doing a rather poor job of it). For two thousand years, Israel served as a physical example of the effects of following and not following God’s laws. For the next two thousand years, spiritual Israel (Christians) have been providing examples of following God’s laws in their spiritual sense.

Miracles do continue to happen within the church of God, but they are small, individual, and generally not reproducible or provable.

It’s only during the end times that spectacular miracles will again be performed. For instance:

And I will give power to my two witnesses, and they will prophesy one thousand two hundred and sixty days, clothed in sackcloth. … And if anyone wants to harm them, fire proceeds from their mouth and devours their enemies. And if anyone wants to harm them, he must be killed in this manner. These have power to shut heaven, so that no rain falls in the days of their prophecy; and they have power over waters to turn them to blood, and to strike the earth with all plagues, as often as they desire.

When they finish their testimony, the beast that ascends out of the bottomless pit will make war against them, overcome them, and kill them. And their dead bodies will lie in the street of the great city which spiritually is called Sodom and Egypt, where also our Lord was crucified. Then those from the peoples, tribes, tongues, and nations will see their dead bodies three-and-a-half days, and not allow their dead bodies to be put into graves. And those who dwell on the earth will rejoice over them, make merry, and send gifts to one another, because these two prophets tormented those who dwell on the earth.

Now after the three-and-a-half days the breath of life from God entered them, and they stood on their feet, and great fear fell on those who saw them. And they heard a loud voice from heaven saying to them, “Come up here.” And they ascended to heaven in a cloud, and their enemies saw them. In the same hour there was a great earthquake, and a tenth of the city fell. In the earthquake seven thousand people were killed, and the rest were afraid and gave glory to the God of heaven.

The second woe is past. Behold, the third woe is coming quickly.
— Revelation 11:3–14

As always happens, the message will generally be lost. God will perform spectacular miracles, but most people will dismiss them and celebrate the deaths of those that performed them.

Some people though, perhaps those represented by the lukewarm church of Laodicea, will recall the biblical prophesies, understand that they are actually happening, right now, and many of them will "be zealous therefore, and repent" (Revelation 3:19).

But until then, the personal miracles of conversion, of healing, of answered prayer, of etc. continue to occur within the Church, but there is no need for them to be spectacular or public.

For a better and more complete explanation, see Why No Spectacular Miracles Today? | United Church of God, which ends with this summary:

Even when God does speak and interact directly with us as He did with the likes of Elijah and Enoch, man will still not repent. No, miracles are not the answer, at least not the miracles you spoke about in your letter, but rather the miracle of true conversion is what man so desperately needs.

Were their needs greater than ours, as you posed in your letter? No. All mankind has the same need—the Spirit of the Living God, miraculously dwelling and working in their hearts and minds. Let us be searching for that lasting miracle, not the fleeting, attention-getting miracles that usually lead no one anywhere.

As much as miracles are great and wonderful, they never have and never will convert the hard, stony heart of man. Only the miracle of the indwelling of God's Holy Spirit will ever perform that miracle. And that is what God is doing today, through the work of His Church and people, as He offers the opportunity for the miracle of a transformed, Spirit-led life to those who are willing to accept that gift—that miracle.

29 Are all apostles? Are all prophets? Are all teachers? Do all work miracles? 30 Do all have gifts of healing? Do all speak in tongues? Do all interpret? 31 Now eagerly desire the greater gifts. (1 Coronthians 12:29-31)

The Apostle Paul gave us reason to believe that most believers would not experience most gifts, so we must depend on each other collectively to hear from God.

Every phenomena on your list except angelic visitation is one that I have either experienced personally or has been experienced by someone whom I know closely.

• The man I know (a dentist named Ross) who saw Jesus personally was healed of blindness due to an injury as a result of the encounter.
• A woman at my church named Lynette prophesied that I would soon meet a woman; I met my future wife a few weeks later.
• On another occasion, I was at a prayer meeting at church when I suddenly felt the overwhelming urge to pray for a woman named Sally I did not know well who had not attended in over a year. I later found out that at the time we were praying, she was on the other side of the world in Papua, New Guinea, in the hospital following an attack by a gang that nearly killed her, clinging for life. I also learned that other friends of hers from around the world were all struck in the same way.
• I once lost hearing in my left ear. While at the ear doctor's office, I was led to read Exodus 4, where God says that he is the one who makes people deaf. I trusted that God was in control and was at peace. Two days later, my hearing returned.

Belief in miraculous gifts is taught in church doctrinally but maintained through personal contacts among believers who share their stories of how God has worked wonders for them.