It’s all about familiarity. People feel comfortable with Windows because they always used it and it has all the programs they always used. Most people just want to get their shit done and don’t care about operating systems at all.

I have Nextcloud running on a Pi4 and it runs like a charm. It has a lot of RAM and processing power to spare, actually. The good thing about arm mini computers is the exceptionally low power draw. You can’t achieve that with some old x86 PC.