Bugs. People that are into linux have enough compium and often the expertise to fix broken stuff that otherwise would work on windows.
Your average user will quit after too many things don't work out of the box.
@Maticzpl Tbf my Windows OS makes me perform a bizarre ritual to just get my headphones to connect each time. Windows has as many bugs as Ubuntu at least.
I also have known people that were non technical that had way worse a time getting drivers to work on Windows than on Linux.
Real issue is software support. A lot of the big closed source stuff only wants to run on Windows whereas most open source stuff is fine working on everything.