Oh, I agree - the show lends itself quite well to crossovers. And I do enjoy some of them. Hell, I've written TS/SPN crossovers myself.

But I admit they're crossovers. I don't just plonk an ex-ranger, ex-cop and his weird sidekick into the middle of a story in another fandom and pretend they're part of the canon. If I take a step back, I can see the logic of those Stargate crossovers - Blair and Daniel have a lot in common, so do Jim and Jack, Jim would certainly be well qualified for an SG team...but those early experiences just put me off the whole idea.