because youd only swap mobos for either aesthetics(expensive, not often done) at best because you choose to downsize, or because you need more pci-e I/O.

the average user doesn't use all their pci-e i/o, and the ones that do, are looking towards workstation motherboards, which is almost a completely different market from the consumer level stuff. It's a game of, you know when you need more i/o, and if you needed it, you probably would have never bought the consumer level board in the first place.