Because those aren't standard and nobody can agree on what the standard should be. Do you want to be the GPU manufacturer that has to make a half-dozen differen

Because those aren't standard and nobody can agree on what the standard should be. Do you want to be the GPU manufacturer that has to make a half-dozen different kinds of the same card for different interfaces? What about the performance over distance? Most of that kind of bus is designed to work well over short distances and much stricter tolerances. These things would make cards cost many times more than they currently do which isn't feasible. Better a "slow" standard that works.