Going back a bit here, but meant to say - I do wonder if it's not actually the same on SA. I've seen a few of the nicer looking girls mention hundreds of messages / being overwhelmed and unable to reply to everyone. Saw a 6 or 7/10 blonde say this on her profile and she'd only been a member for one day.
Dunno about others, but on reflection, I think more than half of the messages I send on SA get no reply.
Women have three options:
Regular dating apps which is great for them because only guys with whom they matched will be able to message.
Sex dating and swinger apps where usually anyone can message them. But they get overwhelmed by messages. Many of my messages don't even get read.
Apps like seeking, where they do get lots of messages but nothing at the scale of free sex dating sites. I have a similar success rate as you on getting replies for messages. But on the other sites, I have received probably two replies in my entire life only for both of them to disappear after the the first reply. Success rate is obviously way higher on seeking because money is involved.
Good looking women do get lots of messages, especially when they are new to the site. But one seasoned SB mentioned to me that many of them are timewasters. Just like female scammer profiles, there are male scammers too and many weirdos. After a month or so, they start getting better at identifying timewasters. That aligns well with my observation of higher success rate with girls who are there for more than a month.