Maybe it comes down to production costs, or something like that? For example, the club will earn x% profit, and perhaps it's so much cheaper to produce the kits with a plain back, it's simply not considered worthwhile entertaining the alternative?
With names and squad numbers, perhaps it's felt too cluttered? The names, sponsors and squad numbers will themselves be a contrast. I appreciate some on here will hark back to simpler times before names and sponsors were a reality.