Why did Buddha need a personal physician?

I can only assume that some things must happen, as Maha Moggalanna couldn't escape his assasins so maybe the Buddha also had to endure some disease.

Every Arahanta is not God. Every Buddha is not God.They never act like "I can control everything. I can do everything. I will never die. I can live forever." which is impossible, imagination. And what you ask is impossible, imagination.

The Buddha and followers are genius, not daydreamers. They know the real causes and effects and get "how we can use life for discontinuing suffering forever" in real life.

Buddha was omniscient and had knowledge over all materialistic things,then why did he need a personal physician?

Our Buddha has only 45 years to help people which he has trained them for 4 Asaṅkhaya 100 thousand MahāKappa, and most of his noble one followers have not more than 100 years to help people in 5,000 years.

If they are genius, they must be experts in how to manage seven qualities of a good man.

So, they chose to teach only importance for enlightenment.

Every teaching and learning have a learning curve which is easy for the Buddha and Arahanta, but hard for the ordinary.

More time more chance. Keep focusing on the Samatha&Vipassanā meditations for speeding the enlightenment. Don't waste focusing on mathematics or physics too much because most people have only 100 years to life.

Get the most out of 100 years of life.

But if the Buddhism will stay forever, he will teach materialistic and physic as well.

Also there are suttas which are to be recited for recovery from diseases which highlight the praises of Buddha,then why couldn't the Buddha and the Arahant Bhikkus protect themselves from the clutches of diseases?

There are eight causes of diseases which no one can't protect some of them, especially uncountable karma causes from past-life.

You must imagine that after enlightenment, the Buddha became omniscient and had become a god or superman of sorts.

I believe this is an exaggeration.

Enlightenment made him fully understand and realize the four noble truths, but if he was here today, he won't be able to tell you how to make a vaccine for Covid-19.

On the other hand, the Buddha and Ven. Moggallāna had some psychic powers, that may have given them some supernatural abilities, but this does not make them fully omniscient or omnipotent.

Having fully understood and realized the four noble truths, the Buddha and the arahats have no reason to find supernatural means to avoid or alleviate physical pain and diseases. They can use whatever means available to ordinary people including the use of physicians and commonly available medicine.

The Buddha and the arahats may feel the physical pain but not the mental pain, as mentioned in SN 36.6:

“Bhikkhus, when the instructed noble disciple is contacted by a painful feeling, he does not sorrow, grieve, or lament; he does not weep beating his breast and become distraught. He feels one feeling—a bodily one, not a mental one. Suppose they were to strike a man with a dart, but they would not strike him immediately afterwards with a second dart, so that the man would feel a feeling caused by one dart only. So too, when the instructed noble disciple is contacted by a painful feeling … he feels one feeling—a bodily one, not a mental one.

“Being contacted by that same painful feeling, he harbours no aversion towards it. Since he harbours no aversion towards painful feeling, the underlying tendency to aversion towards painful feeling does not lie behind this. Being contacted by painful feeling, he does not seek delight in sensual pleasure. For what reason? Because the instructed noble disciple knows of an escape from painful feeling other than sensual pleasure. Since he does not seek delight in sensual pleasure, the underlying tendency to lust for pleasant feeling does not lie behind this. He understands as it really is the origin and the passing away, the gratification, the danger, and the escape in the case of these feelings. Since he understands these things, the underlying tendency to ignorance in regard to neither-painful-nor-pleasant feeling does not lie behind this.

Even enlightenment does not make you free from Karma. Once someone becomes an arahat he/she does not have any need to live but until the past Karma is expended an arahat lives. So in the same way Buddha has told why he got certain diseases and injuries.

Eg:

• A recurring headache because in a previous life as Bodhisattva, he became happy at the sight of a big catch.

• Having to practice strict acsetism due to the insults Bodhisattva (Jothipala) said to Kassapa Buddha.

• Devadatta pushing a huge rock at Buddha, and Buddha getting His foot injured, this was due to a previous incarnation when Bodhisattva had pushed his brother from a cliff due to greed for the inheritance etc...

So many other effects of previous Kamma had to be borne by even the Great Buddha. If a Bodhisattva has done this many bad things in previous incarnations, imagine how much more evil we might have done.

Buddha was omniscient and had knowledge over all materialistic things,then why did he need a personal physician?Also there are suttas which are to be recited for recovery from diseases which highlight the praises of Buddha,then why couldn't the Buddha and the Arahant Bhikkus protect themselves from the clutches of diseases?

Nowhere in the suttas did they say the Buddha "needed" a personal physician. People volunteered their services to Him and He accepted it in the spirit of good will and possibly allowing good opportunity for the donors to practice generosity and attaining great merits at the same time.