The for-life email address was typically a perk given to people who were affiliated with a university when internet was still fairly young (think late 80s and 90s). This was a nice perk, because web-mail was not as common and advanced as it is today. And outside web-mail, email addresses were generally very volatile.

The main reason universities couldn't keep doing this is that they eventually ran out of email addresses. Some may have tried to continue the practice, by adding e.g. some university-specific id to the email address. But this makes the email address much less desirable for using after your graduation. In the meantime, web-mail offerings had become arguably more advanced than whatever the university offered. So it made sense to just discontinue the practice altogether.

I was in the "lucky" batch that got a for-life email address. But it was still an opt-in feature. I.e. when the university decided that the email naming scheme was not sustainable, it asked all alumni if they would be interested to keep their forwarding address or not. Many had already dissociated themselves enough with the university to not take the offer.

At least a few in the UK that I’m aware of (I'd say which ones but I don't really want to dox myself).

University of Western Australia is one.