Linux

If I had to put a name I would say customizability and ease of use. I dual booted for several years, it started as Linux was my programming OS and everything else was on Windows, but organically I started to spend more time on Linux and at some point I noticed Windows had become my gaming system, anything else I was doing in Linux. I fiddled with Wine and some games I could get to run on Linux so I only had to reboot for some games. Then Humble Bundle gave me a few games for Linux and I found other ones that offered Linux builds like Project Zomboid and I decided "you know what? I don't even game all that much, between Humble Bundles and Wine I can probably get enough games to keep me entertained and I don't have to keep dual-booting" so I nuked windows from my system and a short while later Steam came to Linux consolidating my choice.

So yeah, it wasn't that I chose Linux it was that using both for long enough pulled me to one side. I can't tell you exactly what pulled me, but whenever I try to use Windows everything seems so clunky and rigid that I think that played a large role. I remember several times when I had issues on one OS I would jump to the other, the issues in Linux were mostly self-inflicted (even though I didn't knew it at the time), whereas the Windows issues were random, unpredictable and unfixable with time the Linux ones became fixable and even predictable.