A bit blunt but, yeah. Facebook was arguably a lot more cool when you at least needed an .edu address to get on. (Or a bit before or after that point depending on your perspective.)

And a very specific .edu or .ac.uk at that. It's easy to be cool when you are leveraging exclusivity already.

Yes, but my point is that Facebook's ascendancy extended well into the period after Facebook lost it's "coolness," so concerns over FB's decline are overblown.