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.
One different viewpoint to the other answers here: endowments are necessary instruments for most American universities, and are essential for private universities which are not directly supported by the government. They can provide essential resources for meeting the budget needs of these institutions—particularly for costs that cannot be paid for using state or federal funding received. (These can, of course, be supplemented by tuition and other income.)
More importantly, American universities receive lots of money for their endowments because they devote significant resources to recruit and solicit donations. Most universities have some sort of "alumni relations" department to seek out such funds, and typically a development office as well.
I believe a major factor is the experience students have while studying. Certain universities are very good at creating a sense of loyalty, community, and attachment which endures after students graduate.
For example, in the UK, Oxford and Cambridge receive disproportionately more donations than other universities. 41% of all alumni donations in 2013-2014 went to Oxbridge. There are also a large number of named chairs. Historically Oxbridge students have had a strong loyalty to their college and are keen to give back once they are alumni. This loyalty is built through many means, such as the links to tradition, virtually all undergraduates living together in their college. There is a lot of inter-college rivalry in sport, academics, who has the best may balls, etc.
While I have never been to university in the USA, I would imagine that a similar loyalty exists in Universities which receive a lot of donations. For example, College sports in the United States, in particular (American) football and basketball, have a very large following and people are very loyal to their team. For example the University of Michigan has the largest Football stadium in the USA (107,601 seats) and is also in the top ten in terms of endowment ($10.06 billion). Could this simply be a coincidence?
Some universities take a more utilitarian approach. With more students commuting to classes, fewer sports facilities, etc. In this case the education process could seem more like purchasing a service. Not that it would necessarily detract from the quality of the degree/education, but it would not instill the same sense of attachment which would lead an alumni to donate. I would suspect that universities structured in this way would rely more heavily on government funding and attempt to keep costs down by reducing the non-essentials.
Another factor may be that, since in the US the student is very aware of how much the official costs have been offset by scholarships and/or loans through the school itself, many of us feel an obligation to "pay that forward" if we can by putting money back into the endowment funds. Similarly, we're very aware of the non-tuition costs of making the school community and experience what it was, and we don't take a good education and its effect on our salaries for granted; there too we have something of a debt to repay.
Not true of everyone, of course. But for some of us it's real.
There are also the endowments made because someone wants to see the school do something in particular, for reasons ranging from ego to investment in research to you-name-it.
Really, it boils down to "that's how the system has evolved over the past two centuries, as it has interacted with the society and economy it's surrounded by." History is less a matter of grand design than of lots of people making impulse decisions whose sums happen to lean one direction or the other on any given day.
This is an interesting question. There is also an element of high alumni involvement, sometimes a company or individual would want to give to show their commitment to the specific department. Also, often times, those who are major donors can have something in the institution named after them.
Finally, you mentioned "named chairs". These are usually individuals who have an extremely strong research portfolios and that usually have a strong connection with the company as a researcher (in the case of industry named chairs)
Or maybe Americans are just more generous? (joke)
