In the real world, I won’t forget the messages you tell me either, the memories are forever. Why should a digital message expire when memories don’t? I can still remember what my first day of school was, why shouldn’t I be able to see the messages I got sent last week?
I'm curious if you understand that your memories don't expire, but that almost all other people's do? I'd be interested to know if you think the platforms should conform to how your brain works, or if you think most brains work like yours. Just so you know, most people can't remember 99% of conversations verbatim that are years old.
In that case, why do you need a digital message if you remember everything? You also don't have any extra recording on personal communication except your (and the counterpart) memory, why it should be any different for digital messages?
If this premise were true encrypted unscreenshotable apps would be the norm for communication.
They are not. Not even close.
If I tell you something in person, you may remember it for some time, but it's not recorded forever. It exists only in your and my mind. I may misremember or forget it, you may too, and there's no way to know the original message. And there's no way to share that communication. Showing a screenshot of what someone said, is entirely different from saying someone what you heard from someone else. That's why we have contracts because "I said, you said" was never meant to be permanent or enforceable.
This is a feature, not a bug. If human conversations were to be permanent, they would be much less said or written. Messengers, especially private messengers, are a loophole, in a sense that they keep forever what people still unconsciously think of as ephemeral communication, and it's good that Telegram is trying to address it; though I'm not confident how effective it may be.