Why isn't Lent observed across all traditions?

Richard Foster identifies 6 traditions of the church:

1. Contempative
2. Holiness
3. Charismatic
4. Social Justice
5. Evangelical
6. Incarnational

Of these, the traditional Lent celebration is most likely to be practiced by Christians who identify with holiness or who pursue "an ever fuller life of sacrificial, self-giving love". According to the gospels, Jesus began his ministry with 40 days of fasting in the desert east of Jerusalem and so Christians began to follow a similar pattern of fasting leading up to their celebration of Easter.

The Catholic and Orthodox branches of Christianity observe regular fasts, including Lent. The Protestant branch is, as always, complicated. Early Reformers argued that fasting does not, in itself, have the power to make people holy. Therefore required and communal fasts, such as Lent, served no purpose but to give the illusion of holiness and unnecessarily burden people.

Perhaps the most striking rejection of the Lenten fast was the Affair of the Sausages. During the 1522 Lent, Christoph Froschauer, a Swiss printer, served smoked sausage to his workers. Huldrych Zwingli argued in a sermon that since eating meat during Lent was not prohibited by the Bible, neither was it a sin. In other areas of church controversy (celibacy of the priesthood, infant baptism, etc.) Zwingli tended to advocate personal freedom of religious practice.

Protestants who are more closely aligned with traditions other than holiness, particularly those who are evangelical, tend to ignore Lent or only observe it individually. To put it another way, a denomination's attitude toward Lent tends to follow their general attitude toward spiritual disciplines.

The practice of Lent is hardly unique to the Catholic church. It pre-dates the major church schisms. The practice today involves somewhat different implementations in different traditions. Some are much more developed than others, but the general idea is the same.

It is impossible to draw up a list of traditions which do or do not participate, because individual church adherence varies widely inside traditions. A good example I know of off hand is Presbyterian churches -- some of which practice it with as much pomp and detail as some of their Catholic counter parts, others let the season go by entirely unmarked.

I think a more useful question to answer is not the who but the why of non-participation. In my experience I see two main reasons for not participating.

1. Some level of ignorance or indifference.

   Many churches simply don't believe the seasons is mandated in Scripture in such a way that it should be made into a big deal in the life of the church. Others might play along because they don't see any harm, but also don't take it very seriously. Some quite honestly might have just assumed that the practice belonged to some tradition other than their own and never bothered to learn anything about it.

2. Reasoned objection.

   Some churches do not participate on the basis that the practice isn't well rooted in the early church and only became an organized practice several hundred years in. A common direction for this argument to take is argue that the practice originated from a pagan set of rituals (possibly ancient Babylonian), elements of which got folded into Christianity during the time when the Roman empire officially made Christianity the state religion. While some traditions don't have an issue per se with re-purposed rituals, others feel strongly that these are pollutants on "pure" Christian practice.

As a general trend, I think it's safe to say the practice of Lent is roughly parallel to the degree to which churches emphasis liturgy and a liturgical calendar. On the other hand, cults (particularly restorationist ones who believe that not just one or more branches but the entire Christian religion lost it's way after Jesus) tend to be the most emphatic non-practitioners of Lent. In-between you have a vast array of half baked practice and objection.