You can't get the performance of a next-generation device in a 33 watt chip. It's impossible unless Nintendo magically got a chip like 5-6 years from the future. The XB1/PS4 were always going to destroy the Wii U performance wise.
Nintendo could've made a next-gen chipset if they wanted, but they opted to make something around the concept of low electricity consumpion and a small case.
That's pretty much all there is to it.
I believe Nintendo's goal with the Wii U console was always that "PS3/360-level graphics are good enough, what we're going to do is provide a lower power consumption and smaller casing size". That's the design philosophy and always was going to be because the Wii was so successful using basically a chip comparable to the XBox/GCN, just moderately improved. They were always going to bet on the same overall formula again.
