Personally I've said half-jokingly that the redesigns are for job security because admitting that the design is perfectly fine and changes have no guarantee of improvement greater than the adjustment cost would result in a pink slip.

Although that does point to a common problem of 'design for purchasing manager' where software is designed for the sake of pleasing people who don't actually use it and merely adds a bunch of useless cruft that would rapidly become an irritating obstacle to users but looks impressive on first blush.