PalmOS was killed by its design mistakes and technical weaknesses. 16 bits memory limitation, even at the time that was silly. Armlets? Extremely hard to write simple native code or to port apps and games from other platforms. No file system, a custom and rather slow database instead… But they had tons of documents on how to follow their UI/UX guidelines. Basically, they had no real kernel upon which building an OS,…
You're not wrong, but this skips over an even bigger mistake. Arguably 2 in fact.
The kernel of the original 68K PalmOS was, I believe, bought in, just as Apple bought in a Pixo OS for the iPod:
https://apple.fandom.com/wiki/Pixo
PalmOS ran on top of the AMX 68000 RTOS kernel from Kadak:
http://www.kadak.com/rtos/rtos.htm
When Palm moved to ARM chips, it chose not to licence the Arm version of AMX from Kadak. It considered adopting the Symbian kernel:
https://www.theregister.com/1999/10/13/ms_out_in_cold_as/
... but in the end the deal didn't happen.
This was a huge mistake. Symbian was already the smartphone leader and supported multiprocessors, multimedia, and all sorts of fancy features, while being smaller and far less resource-hungry than contemporary rivals such as WinCE or the then-huge Linux. Symbian originally shipped on a circa 8MHz Arm device with 8MB of RAM and no swap: full GUI, full multitasking, Internet stack, etc. No Linux could run usefully on that level of kit.
Symbian already supported GSM phone stacks, Bluetooth, Wifi, all that stuff. It also supported pluggable UI layers, and had about 3 or 4 on sale at its peak: UIQ, a stylus- or touchscreen-driven UI from Japan for keyboardless phones; Series 60, for keypad-driven phones; Series 80, for landscape-orientation touchscreen phones; Series 90, for QWERTY-keyboard-driven PDAs. Adding another for Palm, with a Palm UI and Graffiti, would not have been a stretch.
It would have been a great fit.
Palm decided to write its own instead. Probably it was cheaper. Probably as Palm was mainly American it didn't appreciate that there were tens of millions of happy European and Japanese users with Symbian smartphones that they loved. I was using 32-bit Arm-powered smart devices with the Symbian kernel a decade before the iPhone, and ones running the direct ancestor of Symbian in the early 1990s.
This was commercial suicide #1.
Palm had no multitasking, little media support, and a single-tasking 68000 OS ported to Arm. It was very uncompetitive, but it's all Palm owners knew so they thought it was fine and liked it.
But it did have a comeback attempt.
Palm ended up under the same ownership as Be and the core BeOS team, and it eventually came up with an in-house multitasking media-enabled networked PalmOS, based on BeOS tech, called Cobalt:
https://www.palmsource.com/palmos/cobalt.html
This was commercial suicide #2.
Cobalt looked good but it was too little too late and as far as I know it never shipped on a single retail device.