I would think a big reason is that the version of Windows that ReactOS is based on hasn't been supported in about a decade or more, and there are people who cou

I would think a big reason is that the version of Windows that ReactOS is based on hasn't been supported in about a decade or more, and there are people who could be perfectly-well served by it. Windows' biggest competitor in the past decade or more has always been the previous version of Windows. The early versions of NT were incredibly stable and did a great job while using 1/100th of the memory and disk space of what Windows requires now.