Yeah, I was amazed both when I saw how much water got wasted in home RO and how much wasn't wasted in industrial RO!
There are a few more parts you can buy for the home install to make it more efficient. I can see the manufacturers leaving it out due to install space and cost.
My system is relatively new, but this thread has my thinking of ways I can better use that 4 gallons of waste.
That's handy to know. I was investigating whether I could make my hydroponics system recycle the water but the waste ratio made it unattractive - it was only for science.