"How so?" isn't snarky at all to me. It's a rather legitimate question one may pose to somebody who just said they'd stop using a product but can't. The answers could be one of a wide variety, like vendor lock-in, network effect, contractual obligations, or company policy, no viable alternatives (because...), or something entirely unexpected.

I'd actually be interested in the answer from grand-poster as well, if only because I am a curious asshole.