[Amezarak]

IS there some reason to believe you wouldn't have the exact same problem in a pre-Covid world where people are being regularly exposed to colds, flus, RSV, and every other respiratory virus on a constant basis in their 20s and 30s? Why would losing naive T-cells to Covid adaptions be a bigger issue than losing naive T-cells to the zillions of other infections?

[AstralStorm]

There are a few viruses with this behavior. The ones you mentioned are not.

It's likely just a matter of being unlucky this time that a well spreading virus stumbled upon this way of avoiding immune system which breaks it.

A bad case of Ebstein-Barr virus (a herpesvirus, causing mononucleosis) can set you down for life, for example. Certain bacteria like ones causing Lyme disease can do it too. You don't hear it talked about because they do not spread as readily.