That's a pretty recent change though. Not long ago they used to require a non-temporary email, often a phone number (no prepay phone numbers allowed, ruling out most of many countries), and maybe a bunch of captchas to top it off.
But back then there was no official way to browse more or less public servers, which is the case now. I guess to join those it might be good enough in their eyes to just create a temporary account to let users test the waters and hopefully later convert into a proper account.