Why all the dirty comics? Well, people seem to want to read about them, judging by the site metrics. The only downside is that Google Adsense likes to block ads for blog entries like this one that say "adult" too much.
As for the Mexican sensacionales, they're particularly interesting because the obvious exploitation comes with some blatant self-censorship, too. (Something akin to Heavy Metal's censorship of Druuna, I imagine.)
For example, I came across one such comic showing some fellatio – with chup! chup! sound effects and everything. But as you can see in the first pic below, the woman has her hand and mouth around ... nothing! The artist simply didn't draw the offending part. Context is everything, folks.