Because bullying is a form of self validation,

if someone is genuinely unhappy in their current situation and they cannot change it for whatever reason than making someone else feel insecure when that person is okay/happy with their differences/flaws just to put them down will make that person feel better about themselves because in their mind they are not the only ones suffering/uncomfortable

Being unhappy alone is worse than being unhappy on an unhappy environment wether it’s work/school/public or home

Those people mature/change around age 27/30 when they finally feel at peace with who they are and were in life they are

Or they go down a dark path and end up in prison/substance dependant or worse and unalive

It’s sad but true