Website forums are populated with most of the same people that you'd actually encounter out in the world - EXCEPT that you're more likely to NOT have the most popular, most attractive people here, because they're too busy living their lives. So, you get the normal cross-section except less of the "top-end".
Obviously, there are plenty of desperate, creepy guys in real life, right? So that means you're going to get them here too. Then, the anonymity of the Internet is going to let many of those creepy guys be much more forward and direct than they normally would be, because they are insulated from the consequences of their actions.
Next, these guys are acting from a MALE mindset and perspective - not realizing that women think and work very differently, and have different priorities. In one of the comments, you mentioned not "begging guys to see your boobs or vagina" - well, now many complaints do you think you'd get if you DID do that? Likely none (from guys, anyway), and lots of grateful and happy guys checking out your pics. That's because guys LIKE naked pics and don't need an emotional attachment in order to enjoy them and want them. (Most) girls DO need an an emotional attachment to enjoy a dick pic - they only want to see THEIR guy's dick, and others give them the creeps. These desperate guys don't understand that - they assume that girls work the same way as they do, and will be turned on by random dick pics and such. The fact that a small percentage of girls ARE turned on by them and respond positively to them only reinforces that idea for these guys - they completely ignore the fact that MOST girls are repulsed, and it just becomes a numbers game for them.
Here's the bottom line:
- Only a small percentage of guys do this stuff, but when there are 400,000 regular site users, half of which are men, 20 or 30 guys is a tiny percentage of that total, but to YOU, a single individual, it seems like a lot. It isn't.
- This is a site that specifically talks about sex and relationships, so sexual subjects and people interested in sexual subjects are going to be drawn here even more than an average web forum. You have to accept that additional risk/annoyance when you come here or any site like this.