Because sometimes you want full cold, sometimes you want full hot. Yes you could use a three way valve but you’d generally lose maximum water pressure.
I don’t understand how what you’re suggesting could work any differently than a standard mixer tap, where if you want full cold you turn it the way to cold, and pull all the way to fully open. You say “you’d generally lose maximum water pressure” - how does the mechanism you’re thinking of actually set the ratio of hot to cold, and how does it not lose pressure?
Why would you need separate hot and cold knobs if all that matters is the ratio between them?
Because sometimes you want full cold, sometimes you want full hot. Yes you could use a three way valve but you’d generally lose maximum water pressure.
I don’t understand how what you’re suggesting could work any differently than a standard mixer tap, where if you want full cold you turn it the way to cold, and pull all the way to fully open. You say “you’d generally lose maximum water pressure” - how does the mechanism you’re thinking of actually set the ratio of hot to cold, and how does it not lose pressure?
I’m so confused. What do the cold and hot knows even do?