This one should be obvious, but no one points it out: how long every game takes to fucking release.
Yeah, yeah, "gaymes are bigger now so they take longer to make!!!". Dev teams are also like 10-20x bigger than they were in the 00s, with budgets 10-100x the size, and yet unless you're the kind of manchild who still buys Fifa every year, you're waiting several years for sequels that would've taken 2 in the past. It's impossible to become invested in a series if I realise that I'm probably going to have kids my age by the time the next one comes out, and be dead and buried before it ever ends.
And the main reason they all take so much longer now is pure WASTE. Big bloated companies that are like 30% managers, advisors, and HR she-gremlins bribing jack-off devs who give 0 shits into the office with bean-bags and free Red Bulls. Working in tech myself I can tell you this exact bullshit happens all over the industry, and was the major cause of last year's lay-offs, but it's far worse in gaming because large gaming companies are some of the only places in the world where you can go 6+ years without releasing ANYTHING, because jaw-hanging troglodytes still buy your fucking online passes and re-releases on the daily. If these guys actually had to work for their pay-cheques a little, we'd be seeing dev times half of what they are now among AAA teams.
It's an issue that honestly bothers me a lot more than the general decline in game quality, because at least if you release a shitty game with short cycles, you get another shot at a good game reasonably soon. But when you wait 10 years for GTA 6 or TES 6, the game had better be a fucking masterpiece--and if it's not then the fans can all forget about getting a good one this side of retirement.