In the majority of third-party cables, those were just SCART cables with only the composite video hooked up, not actual RGB cables. You had to go for the official cable.

And the vast majority of people hooked up the console with the included cables and never gave it any more thought. You're looking at the past through rose-colored console nerd glasses. And not all TVs with SCART were RGB capable.

Im looking at the past from the perspective of someone doing computer/console accessories retail in ~2003-5. Additional free RGB cable, memory card or second pad were the difference between average and good console shops. I still have my ps1 and xbox stashed away with RGB SCART cables.