There are, apparently, dramatically more seekers than guides. Part of the issue is that guides usually have no trouble finding one extra player without resorting to guided games, and part of the issue is that there's really no vetting in guided games, so you can't tell if you're getting 5 competent seekers or 5 complete noobs or some weird mix, and you can't indicate what level of guidance you're willing to provide, which scares of many potential guides.

And then there's the sucky part of being a seeker, as you pointed out... You're stuck in orbit, seeking, until it matches you. Which is terrible. You're absolutely right that it should be a background seeking feature, and it should be far more robust in terms of showing people what your experience level is.

The group I usually raid with on the weekends with ImmortalVagabond is actually one I found from the only time I was a seeker in guided games. They are super cool guys, and incredibly patient. We've been raiding once or twice a week together for a few weeks now because of that guided games. But there is the downside in that I sat in orbit for about 48 minutes (just put netflix on my phone and watched something. And guided games seems to introduce a few other issues because of the lack of checkpoints. We ended up having to leave the guided games raid instance and redo two encounters one week because of a bug that you can only really deal with by leaving to orbit.
Though I've had friends say that they sit there for an hour and then had a terrible experience. I'd like to see a more WoW like system for guided games, where you can queue and then run around until it matches you and you get 30 seconds to accept or it rolls to the next person in line.