A trust may be created for any lawful purpose. Every trust of which the purpose is unlawful is void.
What is scandalous is the corruption after the takeover of temples as politicians and officials loot the temple’s wealth and land, and divert donations of devotees to non-religious purposes
If a trustee is corrupt, penalise him. But do not take over the trust. Communities, the world over, have a way of correcting themselves and promoting a vision that best suits them, subject to civil laws, of course. It wasn’t long before that all temple trusts belonging to the majority community were ‘nationalised’. The strategy was invariably the same: level charges of corruption; supersede the trust; appoint government nominees; and control the way ‘donations’ are spent.
The temptation to control these trusts is obvious. There is both money and power — a heady combination.
Now to your query:
a) The reason for takeover by government has been discussed above.
b) Same as above
c) It should be for the development of temple only but government may divert the funds for other welfare schemes too.