Mine is professional feasibility, enjoyment, and ease of use and I see the world through those eyes. I got very tired of spending all those hours in the darkroom on a daily basis, and love working in the light. Half the time I'm on APUG I'm working on the other computer right beside it retouching and printing. I absolutely get that people who work on computers all day are sick of them.
So I agree that the love of the process is a major reason for people to use one or the other.