I've always been captivated by the rare backs, been collecting them for 20+ years. I think Jim B nailed it...more collectors interested in them nowadays and certainly a lot of resources and forums (and threads) covering T206's from every angle. There's also a handful of big collectors working on master sets, which is a beast to do, but there's some out there trying, so that has been driving prices up. I'm glad I got mine when I did.
But, like anything else, there often are cards that slips thru the cracks, so keep an eye open!
