Since posting this, I've found an Imperial Guild that fit for my solo alt (it fell into my lap), but the fact is that I, and at least a small percentage of players out there, want a different kind of guild than is usually presented or advertised on the forums. If you read the ads, they might talk about about casual guilds, but then immediately say 'we do Ops and FP'. That's not a selling point for me, it's a turn off.
Totally agree with you. May I ask what Imp guild you found? I'd like a home for my Imp character, and I have a very similar play style. I solo most of the time, and I don't like feeling pressured to have the best gear and raid all the time.