Okay, then why are the Xr phones less expensive? Is Apple just being generous to people who like different colors?
Because the superior LCD is also cheaper, and the single camera is also cheaper but better engineered. And the lack of 3D Touch is also cheaper but haptics a superior experience, the less ram is also cheaper but saves on electricity which helps the bigger battery last longer. The aluminium is also cheaper but doesn't rust as much as the inferior XS etc.
P.S most 'stamina' phones are actually budget as well, check out android. Not a causation kinda thing, just saying that it doesn't follow premium in many cases.