Really it was just the Palm Pre’s hardware that held it back
I'd argue it was just purely the rat race of "the most apps" where all other vendors lost out to iOS and Android. It didn't matter that it had all the essential applications, as well as having plenty of the fads/gimmicks of the time (Angry Birds, Pandora, et al) natively supported, it still boiled down to the normie logic of "BUT I WANNA RUN ALL THE APPS!" There was also the whole culture sentiment of "if you make a niche Android/iOS app and sell it, you could become like a millionaire overnight" that people seemed to clamor around, as another gimmick economy (as The Next Big Thing(TM) after the dot-com bubble).
There was also the tidbit that most of the operating system (outside of Linux kernel and standard utils) was proprietary. It's only when it was pretty much given up on, that they started to open it up as various open source projects. Comparatively Android was far more open source than webOS at the time.