A medicine can also be off-label simply because of its price - there is evidence base, but the regulator says that the health care system shouldn't pay this much for ailing this medical condition.
Of course that keeps the prices lower. That's the purpose. It also keeps some medication unavailable for some patients. I don't think it's a huge problem, but it's there.
When we look at popular off-label meds and the eventual evidence we often find that they're not very useful, or even actively harmful.