Comment by Analemma_

In Apple's defense, the SOCs on iPads are improving much, much faster than PC chips. Intel chips have been getting faster at something like 5% per year for the last decade, compared to 50% for Apple's A-series. So I think supporting 5 years worth of iPad devices is somewhat comparable to supporting 20 years worth of PC hardware: in both cases it's about a 100x performance difference between the bottom and top, and beyond that I imagine it's not worth it to try and tune an OS for both.