I don't use FB and don't know much about it.

Googling around, it looks like this lifting of the .edu restriction happened eleven years ago in 2006, around two years after FB launched in 2004. Contrary to your own declining experience, this was actually before FB became relevant to masses of people around the world. Most of the FB history and success has taken place "post-edu" now.

Requiring people to have .edu addresses ranges from being bat shit crazy to crudely elitist, unless it's just intended as a temporary limitation as part of a pilot launch, which is what it looks like this may have been?

I'm actually quite surprised to learn about this bit of Facebook history.