It's probably because the OP makes unwarranted assumptions:
> This is why after 50 years it is still a niche language
where "This" is either the REPL or macros, which they do not specify.
It's just as easy for me to speculate that Lisp isn't popular because money talks:
- You have an idea for a piece of software and create a start-up.
-You hire competent Lisp programmers to write that software. Since they're rare, they're expensive.
-The start-up grows because the idea was good and the software works, and somewhere along the line someone sees that more money can be made by cutting expenses on development.
- They shop around and find some outsourcing party that claims to write Lisp cheaper.
- They outsource development, but the software goes down the drain. "Lisp" is now the problem, according to the new developers. But costs are down, growth is still continuing, and they got rid of the weird people who made fun of their Gucci tie.
- People cash out, and on advice of the new developers stuff gets rewritten in the popular language of the day.
- Stuff muddles on for some time, until everything comes crashing down. The cycle starts anew, except now it's clear for everyone involved: don't bother with the software, focus on growth, and in case of doubt:
Blame Lisp!
So yeah, that's my "Why isn't Lisp more popular?" hypothesis: modern software for start-ups is about enabling growth, not quality.
And without further substantiating it's just as valid as blaming it on the "ability to self-modify."
> It makes lisp a terrible experience for beginers.
That might be true.