TV manufacturers didn't have a single, obvious RGB connection standard to implement. Physically, there was SCART (with competing European and Japanese pinouts), RCA, DE-9, HD-15, and various manufacturer-specific DIN plugs to choose from.

Then you have the various electrical signals to send over them such as RGBS, RGsB, RGBHV, YPrPb, digital RGBI, etc.

And VCRs didn't even need RGB because Y/C was good enough. (In fact, I think Y/C is good enough for early computers, also.)

While this was all being sorted out, device manufacturers typically provided an RF Modulator that could work with any TV using standard 2-wire 300 ohm screw connectors. So for the TV manufacturers, their job was already done. Providing more connectors for external devices quickly hits diminishing returns.