It’s not that they can’t, it’s that they don’t have a need to. Enticing news, fake or otherwise, keeps people engaged, commenting, posting, starting flame wars, and they do all of it on the platform. Somebody at some point noticed that users don’t mind fake news (as in they don’t leave the platform as long as there is fake news posted there), and the potential ‘hit’ to reputation is well balanced by the boost in engagement they see.
Lemmy, on the other hand, might not have the same incentive (yet?) to keep spreading bullshit for the sake of getting firemen and arsonists locked in a neverending game.