it might be because of the inherent feminisation of the bottoms that often happen in omegaverse (especially with them being able to get pregnant) that's reinforced when these terms like mother and wife are used to address them.
it doesn't help that the top/alpha is often much more masculine/have more masculine traits like being larger/stronger plus how often omegas r degraded/discriminated in these stories.
it also really drives the idea that romance often involves more "superior"/masculine person with a "inferior"/feminine person. since majority of bl readers are women, having these ideas that the weaker person in the relationship aka the bottoms are linked with femininity and women is off-putting cuz it just shows clear misogyny/gender inequalities that i lowkey don't wanna see in bl with two MEN.
tho idk maybe other people think about it differently, but this is just what i think. i actually despise when they use terms like wife and mum cuz omega males r just dudes who can get pregnant, they aint goddamn women so why use those terms???
honestly it's such a big topic if u think about it and i can't really explain it that well, hope this makes some sort of sense lol

I have a question: please don’t get mad. Why people get angry When the Ukes r called mother in omega verse? Aren’t they already carrying the baby? Why is it wrong to call them mom? ┗( T﹏T )┛