What defines an "unhelpful" answer?

Not trying to start a war with the mods here.

But if I (as the OP) found an answer helpful, why would it get removed if others don’t find it helpful? I am not asking because recent answers on my posts that have been flagged as that made sense, but it has happened in the past. I think something is helpful, I give a GA, then later it is removed.

I have also noticed that if I address two people in one post, if one of the comments I am replying to gets deleted, so does mine. Even though I am addressing more than one person, so now all my writing is gone. Kind of irks me if my response was helpful to the other comment not removed. Is it better I double, triple post? That seems annoying too.

I find subjective modding interesting. I don’t prefer it, but I know it is unavoidable, we all have biases. However, modding a grammar mistake vs. an “unhelpful” answer is different.