If I can't pay for the robots, I am not getting them. And if I buy my robots and you only get a dishwasher then you can afford two nice vacations on top while I don't.
You don't lose anything if I get robots.
Let's say we have a finite amount of cheap water units between us. After exhausting those units, the price to acquire more goes up. Each our actions use up those units.
If restrictions on water use do not exist, you can quickly use up those units and, if you can easily afford more units, which makes sense as you have enough for robots, you are not concerned with using that cheap water up.
I can't even afford to "toil" with my dishwasher now.