You are most likely doing boyfriend disqualifiers too aggressively so girls know all you want is sex. They feel no need to keep fucking a guy, if the option to lock him down is not available if they like him later
"Hey, I'm looking for fun here, you?" - this is my old Tinder opener which I'm not using anymore. I agree with you that being this forward about my intentions could cause pump and dump worries.
However, it has been very different with the other two chicks. And I heard this "If we are going to have sex tonight, I'm not gonna see you again." objection from three of them. Which tells me it's not the aggressive boyfriend disqualification which is causing this. You remember this chick who I presented myself as a husband candidate (it's the second link, you've commented on this post)? Very different frame, the same comment.
When it comes to framing, these three chicks were like this:
1) Fuckboy frame (looking for fun opener) - frame moved more towards fwb
2) Husband frame
3) Connection frame (through Tinder and whatsapp messaging)
My hypothesis about the root cause of this problem is LACK OF SEXUAL FRAME.
Ok, you could argue that 'Hey I'm looking for fun here' opener is as sexual as it can be, but as far as I remember this interaction, that was it. I started the Tinder convo like this and then after it went much more friend-fwb frame (until I started escalating on her heavy and asked her to follow me to the forest).
I'm thinking that the root cause of the problem is cognitive dissonance by seducing in early stages with social/friend/boyfriend frame and suddenly turning on the sexual frame through physicial escalation.
I think the solution could be a well developed sexual frame, especially in the earlier stages and especially the verbal part (sex talk/2nd gen verbals).