I feel there might be something else. The key word here is relationship. We must agree that open-relationships, polyamory, etc. are not the norm. People who might wish to start one such relationship might find it very difficult to come across a potential partner who would be willing to sit down and consider the possibility of other people being intimately involved with one's partner (and what that implies from an emotional point of view, etc.)
So, they come across your profile. What they see is not that you are looking for sex, but rather that you would be openly to consider a non-traditional relationship pattern. They might even completely shut off their brains when they read that part and completely forget that you are in it for the carnal satisfaction. Of course, having gone through so much trouble themselves to find one such partner, they believe that you must have been in the same situation. Just a touch of their magic fan would transform you into a stable-relationship-oriented partner. Which is not the case.
Mind you, that doesn't help you with the fact that these people annoy the sh*t out of you.
Another thing might honestly be that they are low-key negging you. If they clearly see that you are in it for the satisfaction of your physical desires and needs and yet start with messages such as the one you showed us, they might be trying to get a reaction out of you, to demean you and lower your self-esteem so that you would accept them, even if they were not attractive to you.
Something along the lines of: "Look at you, you filthy wh*re. You should be so flattered someone as good, as honest and pure as I, would ever want to approach my genitalia to your sinner's body. Now satisfy my needs."
Just that they choice the worst person to neg they could have picked in this big ocean of free fish that is the internet.