Who decides to hide answers?

It is a software program that decides which are hidden.
No one knows how or why except the person responsible for the software that determines it but there are many theories about it.
It is supposed to be the answers that are not Relevant to the question are hidden BUT that isn't how it happens. Many good answers are hidden.
Long answers sometimes get Hidden and sometimes not, short answers do get hidden more often than not.

Some things for sure are it is Not thumbs down as many believe and it is not being flagged those are just some things we know.
Some users will copy the question in their answer and that stops that answer from being hidden no matter if the answer is relevant or not.
Posting using capital letters on each word or words from the question will keep an answer from being hidden and keeps them at the top of the answers given again no matter how crappy it is and if it is relevant or not.

The only sure thing about it is that is a mess.
They should not have made the default setting Relevant but should have left it as in order of answering.
They do have a sort option if Relevance is clicked and we can see the Oldest, Newest and Highest rated and there are no hidden answers on those lists.

A small computer program that does an algorithm between the question and the answer looking at the answer for relevance to the question. If there is little or no correlation between the two it hides the answer, but gives a clickable link to open all hidden answers.

A computer program decides relevance, and seems to randomly hide some answers.