To be fair, the goal is the same.

1. Not everyone needs the sheer CPU, power, and costs of a 40 GB/s connection.
2. Higher wattage chargers cost more
3. Not everyone needs a USB port that does video out (even if it should be standard now that virtually every new GPU should be compatible)
4. Even if the CPU and GPU support a feature, the OEM can use a cheaper controller
5. The controller firmware can lack support for a feature or be buggy

The USB forum can only solve points 4 and 5 without raising costs on the cheapest hardware.