What weird hentai world do you live in where this is common? As a guy I find neither of these things erotic, but even then it's up to personal taste. There are apparently enough people who enjoy this for the author to keep making them.
Well then there you go: I live in a world where "there are enough people who enjoy this for the author to keep making them"..... and it's our world, not a alternate hentai world :)
If you wanna, visit the E-hentai reader or some other online reader where H manga for boyz are collected, you'll see that the weird-bondage and weird-fluid-production fetish stories are really common