Installing Arch is unnecessarily difficult for most people. Manjaro is Arch without all the hassle. All the "cool" people seem to have switched to Manjaro's successor, EndeavourOS, though, which does the same thing but with a rebrand.

I've never had trouble with Manjaro because of anything Manjaro caused. The occasional error when updating because the AUR is ahead of the distro repo is never a problem. The worst problem I've ever caught them on was "forgetting to renew their HTTPS certificate that one time".

Manjaro has a tendency to fork and ship stuff that works well enough. They don't wait for the last two or three years in the long tail of development before general availability. That makes their software rather unstable on some platforms (mobile, Apple ARM) but on the other hand, their software is actually available, not just a tarball and a makefile.

The biggest issue Manjaro brings is the flood of users who don't know what they're talking about coming to forums like Arch Linux trying to solve their instability issues. Once Manjaro fully dies, those people will still exist, they'll just ask about "how to fix libxyz on endeavour" instead of "how to fix libxyz on manjaro".