Windows, for its many faults, is feature complete and officially supports ARM today. Neither is true of ReactOS. Thus, it's currently much easier and more useful to port windows.
ReactOS is nowhere near enough the quality you'd need - you don't want to waste time figuring out if you are fighting a bug in ReactOS or in your own code.
Agreed. Just last night I tried installing ReactOS in a Parallels VM on Intel, and their ISO installer couldn't get beyond "Failed to open txtsetup.sif" at the very start. The last ReactOS ISO I could get to work was 0.4.11 (three releases / three years ago). It's a worry that such a critical showstopper regression has gone unpatched over 3 years.
0.4.11 did run a lot of Windows software that I use (including my own) & I was impressed with what they'd achieved, but it regularly corrupted the file system and required a full reformat & reinstall, so not something I could actively use.