This thread has been interesting, because you could go back 10+ years to see lots of talk about long-term AI squad building and the quality of newgens/development/reputation (either too good/not good enough/not getting played/not willing to go on loan etc). It's been an issue for years and years, just wearing slightly different clothes - I think I recall even as far back as FM 2007 having the problem of AI squads being awful once current players had retired.
I mean the simple answer to it is that whilst I have no doubt that SI do put some resource into looking at it and making tweaks, it's never going to be a massive priority (and I also accept it's probably a mammoth task to try and fix on such an old codebase). SI will put money and time into stuff that the majority of players are likely to experience - and like it or not, I'd imagine (and be fairly confident in saying) that the vast majority of the fanbase will pick a big club in a big league, play a few seasons (perhaps no more than 5 or 6), then quit and start all over again with somebody new. They will never encounter these issues (and many others that generate a lot of posts on here). This forum is not going to be anywhere near representative of the userbase as a whole in how they play.
I think those hoping for SI and their Sega overlords to do anything to change this are sadly misguided. FM is locked into a yearly release schedule and will always need new shiny stickers to put on the box to give people a reason to want to upgrade beyond database changes. Wasn't it FM21 (or 22?) where one of the touted headline features was being able to influence a nation's youth development, but somebody ran some really extensive tests and the actual impact was close to 0 - and it was confirmed by SI that it was working as intended? Again, most players would never, ever play long enough to ever see anything from that feature (even if it did drastically change things), but it sure sounds like a good thing to have!
I don't really blame SI, they are working within the constraints placed upon them, not just by Sega, but the userbase too - whilst people will say they would prefer SI to skip a year, I don't think the majority of players would. Besides, it would be commercial suicide, especially when, as I say, the vast majority of people won't even see/think/care about any problems.
The only thing that would ever see significant change (perhaps even building a new game from scratch) is if a worthy competitor showed up and started eating SI's lunch. But which companies can you see wanting to put in the money to take SI on? I can't think of any, and so this cycle will continue until enough people stop talking about how 'this will be the last time I buy it on release' and, you know, actually stop buying it (and the irony there is that if too many people stopped buying it, there's even less incentive for Sega to want to provide enough funding needed to fix everything).
And so the world continues to turn.