With mainstream languages, there's rarely any single clear and/or insurmountable problem, it's all the little annoyances you run into every day that add up, plus the cognitive load imposed by the language directly as well as indirectly through the code it lets you write.
I'm not 100% up to date on how much PHP has closed the gap in the last few years, but subjectively I never found it anything but tedious due missing features, various unnecessary pitfalls (sometimes with security implications), silly limitations (you can write a static type in this case but not in that, you can catch this error but not that, no inner classes, etc etc.), and numerous other small cases of poor "ergonomics".
The "batteries included" nature of the standard library is nice, and in contrast to the somewhat fragmented world of RubyGems or NPM it can feel downright pleasant, but finding a SQL library or such is a pretty small effort in the scope of a project, and (popular) 3rd party libraries tend in my experience to be better than the equivalent standard library stuff in most of the languages I know. Every time I wrote a non-trivial amount of code with PDO, I had to look up the correct initialization rituals to get sane settings and copy or recreate a bunch of more or less "obvious" helpers. I'm sure there's something better in Composer by now.