This is amazing! Thanks!

You might like this (if you're not already familiar with this masterpiece) https://youtu.be/_-BjC1GHwPY

It is. But the reality of those sites is that for a guy the vast majority of your messages will never be read. You are shouting at the void and hoping for the best. This does not incentivize taking the time and psychological investment to write thoughtful messages, because you will send comparatively few and the lack of response is harder to deal with when you're more invested. It incentivizes sending the quickest messages that you care about the least to as many as possible. The guy didn't send her a dick pic, he sent every woman in a 50 mile radius the same dick pic hoping that with enough sheer volume he'll get a response.

It's basically spam that wants to fuck you, because non-spam options don't get you anywhere.

A picture is worth a thousand words

"Hi I am...I am looking for sex"

If you are using a dating website and actually trying. You'd look at a profile, read their bio, and then send a message that had something to do with their bio. (Could also comment on pictures)

But it is a numbers game to an extent and most messages sent will never see a reply.

So what is the least effort highest reward thing to send first? Private picture.

They are hoping that the person opens it and it catches their eye.

If their first thought is to send a private picture, they are not really looking for small talk. So it has the added bonus of weeding out non-sexual people.

It's no risk, high reward

the principle equivalent genital exchange.

they think if dick pic is send vag/boob pic will be the response

Or they just think if they see tits it makes them horny so women MUST be the same way?

This one. The problem is that by the time 90% of the hetro cis male population of one generation has figured this out, a new generation of teen hetro cis males are right behind them. A better sex education class would cover this.

They're called posts.