I've been working on a hobby OS for a while now; I don't expect to ever do any major graphics work[1], and I do want to run on ARM eventually, but it's just so much easier to get started on x86. x86 has a lot of baggage, but it also has a rather simple text mode, and easily accessed serial ports which get output easily. And there's a whole bunch of freely available documentation from Intel and the community that helps a ton.

[1] At some point, I probably have to do bitmapped text, but I'm trying to keep my scope narrow, and graphics aren't for me. :)