Probably because not enough ppl use it to make a tutorial? Or don't wanna make one for free...Most of the time other than like the 'official' Vocaloid channel, the 'tutorials' are always made by western people as opposed to a Japanese user (maybe they don't think it's worth the effort or wanna share their 'secrets'? [While there are ppl who share their off vocals I think ppl intend it more for utaite covers because Japanese composers also don't share VSQs the same way some English using composers do lol])

That said, maybe try to find some covers/usage of examples you like, and comment/ask those people directly for advice?