Why do American universities receive lots of endowments? The amount of endowments that American universities receive is much more than European counterparts. Why alumni of American universities and other people have such a big desire to donate money to universities.

This happens in Europe too, but much less than America. Almost all American universities (at least major ones) have many named chairs (funded by external donors), but you see it rarely in Europe.
There is a greater tradition of alumni giving in America, which European universities are trying to also foster (especially in the public funding cuts to universities seen in the UK).

In America there are also generous tax breaks when giving money to charities and foundations which encourages gifting.