A language with a new and unfamiliar syntax requires that you unlearn all these key-bindings and start thinking on the level of tokens again. It's understandable that given the choice, people who have already graduated from this stage would rather not repeat it.
It's sort of like one of those keyboards where the semicolon key is elsewhere or the PgDn button is bigger.
Once people graduate from the "I'm going to learn ALL the things because it's fun and I got surplus brainpower", they usually discover that there are lots and lots of problems out there that require plenty of brainpower and people will actually pay you for solving. It's somewhat silly to allocate your mental effort to things that get you nothing but intellectual gratification when you can allocate it to things that get you intellectual gratification and monetary compensation that will let you do many things you otherwise can't.
Learning syntax that isn't going to pay me back? I don't have time for that.
Having to think about the syntax is like not being a touch typist. Sure, I can still press the right keys, but I have to think about doing so, which slows me down and takes my thinking off of what I'm trying to say.
The kind of problems that they help with are actually fairly rare, while their disadvantages are expensive. Basically the syntax sucks and all the really useful bits are now in all the other languages any way.