Because it will be inevitable that someone with less power will enter into the relationship out of compulsion due to (real or perceived) no other choice, and not because they want to.

in employment, yes, I am suggesting that, and that the basis behind at-will employment is flawed, there are plenty of ways to allow for the paid-person to exit a contract whenever they want without it meaning the company fires them whenever they want for any reason.

in other contexts, no, I am not suggesting that, but there are some fringes that try

The McDonald's CEO is gone because of a consensual relationship where the power dynamics were unbalanced

And how do you even measure 'power'?