I guess it's because we tent camped and then had a van width B. At 101" wide our current C is plenty wide enough so we really don't need slides. Mechanical reliability is not the only thing to consider. Each slide adds 500 to 800 Lbs. to the weight of the rig and puts many at almost limit with just fuel and passengers. We also cold weather camp on occasion which is the last place I'd want to have a slide out. Still it's all up to the user. If we were full timers, parked in one place a lot, and followed the sun it might be different.