Live action role playing games are great fun when you have a group of friends over. You each get to portray a character.
Maybe if you are okay with making a fool out of yourself. I don't think I could play those kinds of games.
Well, if you ever played doctor or astronaut or police officer when you were a child, then you have played Larps.
Well it may have been fun then, but there are adults that still play those kinds of games. I'm not into those games now.
Play is typically a childish activity, but psychologists tell us that play can occur at any stage of life, and even among other mammals, so don't exclude yourself from fun
Yes play is most often associated with children, but adults still like dressing up as characters and going to festivals and such.
Perhaps they dress up for evolutionary reasons.  In other words, to find a mate and procreate.  Let yourself have some fun.
Everyone has their own idea of fun, just because someone doesn't take part in role playing activities, doesn't mean they don't like to have fun.
Well consider this:  perhaps they dress up because they do not feel physically attractive or aesthetically pleasing.  t least let them enjoy their lives, even if you are confident about your physical appearance.
There is nothing wrong with it if someone else wants to do it, just not my idea of a good time. People have fun in different ways, to each their own.