People who find it hilarious, like that Ryllharu asshole.
Again, there is a very fine line between stuff like Qwaser, Queen's Blade, DxD, Daimidaler, Ladies x Butlers, Sekai de Ichiban Tsuyoku Naritai and trash like Maken-Ki or the Elfen Lied manga.
I'm not 100% sure it's even something that can really be quantified, but if I had to guess, it is something about pandering to fetishes instead of doing a few well.
- Qwaser (sucking on titties)
- Diamidaler (rubbing titties)
- Sunabouzu (appreciation of big titties)
- Daphne in the Brilliant Blue (skintight clothing)
- Sekai de Ichiban ("girls in agony" ...their words, not mine)
- Those Who Hunt Elves (stripping elves)
- Even series like Brynhildr (foot fetishists, he only gets kicked in the face, never slapped)
All of these are fine, because they pick something, and do it well. Some of them are even quite over the top, but the manage to keep their plot going while still centering around their particular fetish to exploit.
Stuff like Maken-ki or the Elfen Lied manga just throw everything at the viewer/reader and do none of it well.
- Maken-ki has characters that cover a half-dozen fetishes each.
- The much-worse-than-its-anime Elfen Lied manga just goes into random shit in the latter half for no apparent reason at all. There are characters that are shoehorned in merely to hit the fetish bingo.
These kind of series fail because their purpose becomes the ecchi variety, and they are too busy trying to appeal to all the perverts that the plot becomes secondary. Characters have no depth, they're just tick marks on a checklist. Even their fetish appeals are pushed aside simply so they can hit on more of them. Quantity over quality. In the end, these kinds of series do nothing well.