Tunecore is very easy to use, but they charge $50 per album per year. For some people (me), that's much more money than the album would profit, so we just don't put it up there. I used to use Tunecore back in 2008 when they only charged $20 per album, but I was only making about $25 per year on each album, so the move to $50 would have put me in the red. Especially so considering that I only had 2 albums at the time, and any new releases would just make things worse.
I moved all my stuff to Bandcamp last year; I figure if it's good enough for all the big name composers like C418 and BGC then it's good enough for me. They charge around 7% (I think) on all sales, but there's no fixed price upkeep like Tunecore has. And you don't have to pay the iTunes 30% fee on top of that. Unfortunately, my sales have gone down to zero since the move.. but I don't really care to be honest; they were selling near-zero in iTunes at their peak, and I've got my share of the app revenue side of things. I'm actually planning on making Trace 2 OST free for a while once it's released, to try and give the app a boost in the charts.
BTW, if a dev has a soundtrack that you want but isn't up for sale, send them an email. We (composers) have archives of all our music just sitting on a hard drive somewhere, and would like nothing better than to throw a quick zip file together and send it to someone who will enjoy it