I suspect that a lot of people would stop using Tinder if they became aware it was possible to pay to boost your
"position". People don't want to think that the person they matched with got there by paying lots of cash.
The more you use it, the more it knows your type, the more it recommends them, then it dangles out more possibilities that are just beyond reach but could be accessible if you just throw money at it.
The prospect of matching with someone you find very desirable keeps you swiping, making you more likely to do it in the future.
I'm not sure if this is necessarily unethical, but it is clearly an example of a knowledge-based power imbalance. Because I am quite sure the majority of Tinder users are unaware of all the machinations behind the curtains.