Like fraternities and sororities, alumni associations, are really an anachronism. They were originally created and patronized with two foci. 1) as a development (money raising) tool for the school and 2) a tool for new graduates to network with established graduates based on the sense of a shared educational experience. “You went to X university? Oh, me too! I’ll hire you
into this well paying job over that other guy who went to Y university.”
Although these are still the driving forces behind alumni associations our ethos today is that people should succeed or fail on the job market based on their own hard work—not based on their ability to curry favor with a fellow alums.
As (some) universities have grown to offer more and more amenities (theatres, gyms, other recreational facilities) they have sought to cultivate ongoing relationships with alumni by letting them use those facilities after graduation via the alumni association. For successful alumni, this relationship eventually translates into the graduates making gifts to the school. Of course, many graduates do not live anywhere near their alma mater. Of the four schools I attended three of them are on the other side of the country, and I have only revisited two of the campuses once in the last ten years. But as you get older it is nice to get the alumni magazine in the mail every quarter and learn about what is happening on campus. This is especially true if you are a sports fan and your school has a big athletics program.
If you have kids, one also starts to think about how nice it would be to send your own children to the school(s) you attended. In effect, people like the idea of cloning themselves because they see it as a way to validate the choices they have made (there are many examples of this all around us). If you send or encourage your child to attend the school you attended chances are you are a member of the alumni association. Schools love it when that happens.
Some alumni memberships are automatic once you graduate. Others make you pay a fee.