The problem is only in new people not joining the game.
Advertising is the key word.
Not sure if it's off-topic to consider why people are actually leaving this game considering the title of the thread, but it's more than advertising. Imo, it's the turnaround to have a capable team. If they could reduce it from the current 2.5-3 years irl to 1-1.5 years, I think a lot more teams would stick around and experiment in different builds. Before teams used to do it by daytrading, but if they would prefer it done through training, they need to speed up training. And this is from someone who spent the last 2-3 years rebuilding my team. I would happily exchange the value in my players and bank account to have a more functional game that folks can experiment around with more. And of course, keep punitive measures against hoarding money and buying a high salary team with taxes.