I don't think it's entirely true. Many have managed to create alternatives that have gotten serious traction. There's a few I've been consistently playing for a week and honestly enjoying more than Wordle itself.
I've been playing Quordle, and sometimes it's more insane alternatives [1] [2]. I've also really been enjoying Semantle [3], it's probably one of my favorite and most unique ones. There's other ones that are also need but maybe too much, like Squabble [4] and Squardle [5], but I wouldn't say they've all failed.
Also, to say "the game itself is mediocre at best" seems ridiculous. A mediocre game doesn't get popular purely based on once a day and sharing...
I've really been enjoying Quordle. When I first saw it I thought it was just another clone with an interesting gimmick, but something about it just works so well, it's really fun to play. Going back to the original Wordle almost seems boring afterwards.
It's also one of the rare offshoots that actually iterates on the UX experience and improves on it. I like being able to see if a word exists without pressing enter for example.
Mastermind and alike have existed in many different forms over decades. None of them became as popular as Wordle, not even close. It's been mediocre and outdated for a long time. But, Wordle has features that makes it unique, welcoming, and viral. The alternatives you quote aren't even close. That doesn't mean none of them can catch up with Wordle. I was saying that most of them was getting it wrong (like removing daily word limits, making the game harder, more convoluted, asking for signup, adding ads, etc). Nope. That's not going to work.
