How do men get raped in prison if there are security guards?

Because there aren't enough guards to watch everyone all the time.  Nor are they going to routinely be in the toilets and showers.  Imagine how expensive that would be.  And there is a lot less of this than people seem to think, as I know from being an ex-prisoner.

This happens less than it used to because guards are better able to use technology to surveil more parts of these facilities. But in any penal institution there are always a lot more inmates than there are guards and the guards can't be everywhere all the time. Then there are the cases where guards have allowed this is happen as a way to pacify some of the more violent elements they're charged with monitoring.

Because there is one guard to every 20 or so inmates.

The same way someone can have a suicide performed on them while in prison.

The guards are either complicit in the act or coordinating it.

Something like gang rapes on the outside that isn't supposed to happen either.

😄

There aren't enough guards and some guards work for the inmates.

Don't you watch prison movies and shows? I have since I was a kid. I think Shawshank Redemption and Oz were some of the earliest that scarred me for life.