I suspect some are looking for certain things and are not willing to say even over PMs. When they find out that isn't your interest, the block is used to count you out for possible contact.
In other words you are a possibility until proven not. They let you mention how you feel about the subject first though.
I have noticed when I mentioned that I insist on consent, I sometimes get blocked. They want someone that is open minded in ways that I really won't be.
Consent is just one situation that could be applied to other situations.
Another situation might be a sub looking for a dominant. If I were to mention that I was a switch, which I am, that would be another block.
The list could be endless though. Even political reasons.
A way to get around some of this is to put much of this in your about me. Then refer that they look in it for that type of stuff.
That will be a no go from the start. They don't want to read. So they might block you right away. They want to control the subject in a covert manner.
