Am I missing something about Teacher-Student relationships?

It always confuses me when Teacher-student relationships are usually tagged "vanilla" when in real life it's controversial and teachers have a high chance of losing their job. Does anyone know why it's usually tagged vanilla? Am I overthinking it? I'm pretty sure teachers in Japan aren't allowed to have a relationship with their students XD

EDIT: I'm not really big on Vanilla, It's just an observation.

The majority of vanilla stories are cute and romantic, involving only one boy and one girl falling in love. The total opposite of BDSM, netorare, or guro. By your example incest and vanilla shouldn't be together either. Vanilla just means m2f with romance.

Theoretically you could have a loli vanilla guro manga. I can make that happen.... not here but meh.
anyways here a vanilla clip.

What freaky said. Using your logic, there should be no vanilla incest stories, but there are plenty of those.

well...yeah... I think loli/shota with an adult partner and incest shouldn't be vanilla either XD but I get the logic now...as long as the individuals fucking "love" each other then it's more or less vanilla.

Yeah, I more or less get it now. Basically as long as the couple "love" each other then it's basically vanilla. It just seems kind of weird to see something like a loli/shota with an adult partner and then slapping a vanilla tag on it since I don't consider that "vanilla". I always thought Vanilla was literally bland or normal sex. Ain't nothing bland or normal about a teacher-student and loli/shota relationship lul

To be fair, vanilla normally does mean normal or standard but for some reason in the anime community, vanilla has grown to mean lovey-dovey stuff and Fakku has adopted that as a tag, so ¯\_(ツ)_/¯