Back to the question at hand, I THINK he's asking why we still use mechanical linkage between a servo & the carb vs. making a special servo that would be PART OF, or mount directly on, the carb?

That's a good question. Vibration & fear of 'stuff' permeating the servo are not really issues anymore (that aren't easily addressed). Servo motors don't really need geartrains anymore (that's another question/issue), and throttles have always required barely any force to do the 'throttling'.

Mfgs could (should?) integrate a motor & even some control circuitry directly into the carb itself.

My guess is that the reason nobody's tried this is similar to the one that prevented the switch to 2.4mhz/spread-spectrum/signal-hopping radio technology 20 years after it was integrated into $20 cordless phones.

People (users AND manufacturers) in this hobby don't really cotton to newfangled ideas. It's the car guys...and a company who never made a single hobby product; Nomadio...who dragged the RC world kicking & screaming into the 20th century.