The concept of Manjaro is in my opinion perfect, because in theory it allows to enjoy the latest and greatest software while minimizing bugs. But the execution has so many flaws.

• The graphical package manager Pamac has DDOS'ed AUR twice.
• Manjaro mirrors Arch packages and holds them back, so it trails a few weeks behind Arch Linux. But Manjaro does NOT do this for AUR, which results in breakages and results in the next bullet point.
• Pamac offers users an easy way of installing AUR packages but this makes Manjaro vulnerable to breakages for unknowing users.
• Manjaro's website's SSL certificate has expired 4 times. This required users to roll back time to receive updates.
• There has been controversies around the treasurer of Manjaro as well as Manjaro establishing a company and becoming for-profit.
• Some editions of Manjaro are infamously problematic. For example Budgie does not recommend Manjaro, citing its flaws. GNOME edition shipped a Firefox theme extension which wasn't supposed to be used in production because Firefox updates quickly. At one point, the extension broke.

mrvictory1 already posted a lot of these, but there's some extras in here, and if nothing else there's extra credibility from so many people saying the same things: One, Two, Three, Four

TL;DR: they have a bad track record, their packaging lifecycle just plain sucks, and there's so many better distros that you could use instead. EndeavourOS is an easy in-place substitution.