I too have been wondering the same thing as the OP. To be precise, why is USB 3 (.1 or .2) Gen 2 still not common on products like motherboards?
Last year I bought an Asus Prime B450M-A II motherboard for my son. One of my reasons for choosing this model is that it has two USB 3.2 Gen 2 ports. Since then, I've bought two more of the same model, one for my other son and one for a nephew. Now I've bought a Prime B550M-K for myself, also with Gen 2 ports. Neither motherboard is an expensive super-duper model.
I ran a test with an external NVMe SSD adapter specced for Gen 2 and there was a big difference between Gen 1 and Gen 2 ports. I got 500-ish MB/s on Gen 1 and 980 MB/s on the Gen 2 ports.
Admittedly there may not be too many peripherals that benefit from Gen 2 speeds, but if they can include it on a $75 mobo, why not on more models?