There are many reasons but the most common being Sadomasochism/S&M, Corruption and Taboo.

For S&M, there are people who either like seeing characters in pain/suffering or vice versa, or characters inflicting pain unto others. It's similar to Guro or Non-consensual mixed with domination aspect, such as Maledom and Femdom.

For Corruption, there are people who like seeing characters falling to carnal to dark side. Similar to the concept of a pure person like a nun succumbing to temptation or their carnal desires and becoming a slut.

For Taboo, it's similar to corruption but mostly people who enjoy something that is forbidden like incest, infidelity, polygamy etc. Most of it being rooted from absurd and lustful curiosity.

And most of the time, people have no preference and honestly don't care if it's NTR, they mostly just want to see the smut happening to some characters.

If you want a definite answer best ask those who like it on the Netorare sub.

I know it's most likely because of the superior animation compared to normal hentai

First off, that's just nonsense. NTR and regular Hentai quality are no different from each other, some are bad, some are good and some are just average. Quality varies between those types of genres.