Combination Color and Contrast Control
 

I've noticed on a number of the early color TVs that the Color Intensity Control is often ganged with the Y Contrast Control. That makes sense since the greater color, the greater the Y contrast needs to be.

Why was this design stopped? Was is like DC restoration in that the average customer couldn't tell the difference? Was it the cost? Was it both? (Was Muntz lurking in the shadows?)

Do you mean mechanically ganged together on the same shaft? Or done electrically in a switchable 'preset' mode?

The RCA prototype model-5, CT-100 based on it, some of the 21CT55s based on it, and some other sets based on those usually had 2 chroma level controls, one mechanically ganged to the contrast the other independent.
I suspect the reason this faded was a he desire to reduce cost and complexity...the CTC-5 and 5 were both cut down designs from their predecessors.

The OP is incorrect in assuming this practice died with the early color sets. I own a 1971 Zenith 12B13C52 hybrid color TV and it has no contrast control, but instead a control labeled "Chromatic" that control is a 2 gang 1 knob pot that's both 1 of 2 color level user controls, and the only contrast knob....Just like a CT-100 only with a gimmick name that clues the user in to what all the control does.
There may be other examples in newer and older sets, but the Zenith is the one I know about for sure.

Yes, I meant physically ganged together. By 1971, I had gotten out of college and quit working on TVs so I didn't have the opportunity to see any of the Zenith hybrids. I just remember seeing the ganged controls on a number of schematics at ETF.

In later Zeniths with analog integrated circuits, this became the "Picture" control, IIRC.