For some customers, they looked at the resources needed to migrate, and decided it was cheaper to stay put and/or invest the resources that would be needed elsewhere in their business.
Yes, and the reason is that they stupidly painted themselves into a corner and never thought about an exit strategy. Had they been thinking about the possibility that they might one day need to migrate from the beginning, it would be much cheaper to do so now.
That's the thing about painting yourself into a corner, a little better planning at the start can always avoid it with little to no additional effort.