So I've been checking lately Steamdecks and handheld PC alternatives, and comparing them to the Switch, it is weird that none of the other platforms has adopted a joycon style system. I get this not being the rule due to costs, but I imagine having the controllers always attached to the system would be quite a pain if they ever break, plus joycons feel more convenient when playing docked. When the Switch came out and was an initial success, I imagined this would become the norm at a certain point, but I cannot recall any PC handheld system with joycon-style controllers. How come?

The Lenovo Legion Go does it IIRC. It also has a much more ergonomic mouse functionaly built in than the Switch 2.

I just generally don't think it's necessary.

Most people on these things will have their own controllers. And i dont think they're interested in the tabletop multi-player stuff.

I think the draw of consoles is that they're an all in one solution and the joycons are like a Swiss army knife to get there. But I dont think the people buying other devices are looking for that generally.

As posted above Legion Go does, Onexplayer 2 also did, not sure if any other Onexplayer handhelds have had them.

Cost is one reason, integrated wired controller will save money compared to having two detachable wireless controllers with their own batteries etc. But mainly I think it's because the demand for that feature isn't that high. I think most people would prefer to just play with a standard gamepad they likely already have then use detached controllers for docked play.

I would hope a $700 system would have some niceties. 

It really does, TBH. Only the GPU is a bit lacking on the base model.

I'd still wait for the next gen Steam Deck, though.

The Legion Go is awesome, easily the best out of all the PC handhelds out there. I barely use it anymore since my Switch 2 arrived, but still. =D

Removable controls isn't really a must-have feature.
Keep in mind that PC handhelds:

* Are secondary devices, meant to leverage already established game libraries from years of PC video game hoarding. - One game library, multiple form factors/devices.
* Are easier to repair and upgrade in general.
* Removable controls tend to be a weakpoint in terms of durability. I.E. Wobbly rails on the Switch.
* Primarily a portable device, not a docked device, that's what your Desktop/Laptop is for.
* Costs. Removable controllers require Bluetooth controllers, batteries, extra sensors and more... PC Handhelds are already costly.

Not to say there aren't PC handhelds with removable controls, Legion Go for example... But the Asus ROG Ally and Steamdeck have outsold the Legion Go, which harkens back to the above points.