Maybe (probably) I'm a bit rubbish at this, but I've really tried.
E.g. today someone sent a message about one of my pictures. At least they tried to make it about me/my profile, rather than the How ru messages. So I sent a reply asking a question. He came back and we had a total of 6 messages, so not OTT. Then his last response is just a statement with nowhere to go next.
I've had a few of these, seem quite friendly, didn't ignore a message, but it's almost like they've set it up so I'm the one who doesn't message back.
Also, how many messages is normal before "someone" suggests an actual conversation/meet up.