Windows is much more prone to crash due to the accumulated amount of functions and 3rd party reliance it has to be capable of performing.
I had a Unix system (SVR4) that I had accidentally deleted the boot files, it was used as a server and my development desktop, we had it running 24/7 for over 2 years until we had to update it. Admittedly knowing that it wouldn't reboot meant I double checked everything but the system was clearly stable
I don't remember ever having a crash on CP/M or ZP/M apart from one particular program (I think it was called ZIP but it wasn't the archive program) but I had regular crashes with MP/M even when it was doing relatively mundane stuff.
The reliance on active operating systems is going to introduce instability on any program, it is better to obtain the functionality that you don't want to program from libraries. Complex operating systems with many background functions are bound to to increase the risk of instability. Background functions should be minimised or even abolished if you want stability - it is possible to multi-task with a very minimal amount of background tasks, the multi-tasking switcher I wrote was only about 400 bytes and nothing else ran in the background.
I laugh at firefox, despite their boast of sandboxing some less stable functions, its quite easy to lock it up totally - I think they have a different idea of what a sandbox is from me.
There are many millions of PLC and micro-controller programs running which are stable. There are far more computers running which are unstable.
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