For example, how many of those NFTs would have been lost or stolen — and do you want to tell potential buyers “sorry, nothing we can do about it - blockchains mean no margin for error!”
If a developer wanted to market games by offering inducements to players of other games in the form of unique content it seem like a lot of other solutions would be more attractive than the blockchain. Partnership with other developers or platforms like Steam gives you an actual marketing channel to hype the special add on for Tomb Raider players, and to a lot more than 20k people. The only case where I can see them preferring to attract small numbers of players of a third party game who paid that developer for NFTs rather than every player of that game is if their game is pure pay-to-win bullshit and there's no point in targeting the sort of player who doesn't buy NFTs...