My main reasons were I felt arch had changed it's philosophy over the years, moved away from the real keep it simple idea, and started to move more towards making it easier and more accessible for other people, which I felt was dumbing it all down and just didn't have the same attraction for me. Then the more tangible reasons were I felt systemd was over kill for what it does, wanted to try something simpler and more readily adjustable, and also I found quite a few breaking up dates, with arch trying to be almost bleeding edge, updates would come out that broke my system. Void offered a solution to all that.
Still rolling release but not bleeding edge, so updates have time to be made safe first, runit is so simple and easy to understand, and the setup is only whatever you make it. It reminds me of arch from 15 years ago.