You don't know the situation regarding those games. They could:
- Actually have permission, or be of properties that are currently friendly to fan games - note that in the the latter case the owner can change their mind at any time without notice.
- (Probably most likely) the owner simply isn't aware of them at this time. If the game becomes more popular and the property owner becomes aware of them the game creator could suddenly be in for a world of legal pain.
- Maybe the property owner is aware but has decided not to acknowledge it for now. This could be waiting for more value to future legal winnings, or it could be because they think the game is cool but don't want to invite further fan games by officially acknowledging it.
You also don't see the overwhelming majority of fan games that are taken down. It usually happens quickly and quietly without much fuss.
If you want to risk wasting your time and effort and potentially making large financial losses that's your decision, but the fact that other fan games seem to be tolerated doesn't necessarily mean you'll be ok to do the same.