They say that imitation is the highest form of flattery, but that's probably a lot easier to say when you're the one doing the imitating, rather than the person being ripped off. That's probably why there are so many cases of artists accusing major franchises of stealing their ideas or their artwork or just straight up lifting their entire story without any sort of credit at all.
Just look at Disney's history with accusations of ripping smaller creators off. There's enough material in there to warrant a full dossier on the "creative coincidences" they've got away with over the year (or haven't, in some cases) and they're far from the only studio to have fingers pointed.
Sometimes, the similarities in movies are made even more stunning by the fact that the imitating film-maker seems to have totally got away with it. Sure, fans might scratch their heads and draw parallels, but that's not the same as anyone actually being taken to task for plainly copying off someone else's work...
8. The Hunger Games
Ripped Off: Battle Royale
Both of these Kids Fighting Each Other To The Death For Entertainment Purposes movies are set in alternate futures where a shady government uses the death games as a means of terrorising the populus. In both cases, there's an unhinged leader pullling the strings, the "games" are controlled to stop kids escaping and there are psychotic volunteers. There's also a love story to balance the hyper-violence.
If you can't see the similarities - or how similar The Hunger Games was to The Running Man - you're probably not looking close enough. Hell, the protagonists both have dead fathers, which was all apparently a coincidence as the Hunger Games writer Suzanne Collins claimed she wasn't aware of Battle Royale when she wrote her novels.