I think Doug's probably close to the truth..................it looks easy to clean................they do so for a year and call you when it's damaged, but you'll make more from a damaged suite than one that just needs cleaning!
Every time I clean carpets and see a leather suite, I tell the client about our leather cleaning service and ask how they maintain it. The discussion that follows, often results in a job, directly, or by referral.
I reckon you could get near enough full time leather work if you had premises and high visibility.