Roughly speaking laws are established because the consensus of opinion is that certain things are undesirable. Those things can be more serious or less serious but on the whole society agrees that they should not be allowed. Society works because generally we all follow the rules. When someone doesn't follow the rules society takes action against them.
Undeniably walking around naked is something our society has decided is unacceptable. This man knows that. He knows the consequences of his actions but chooses to be naked anyway.
I would have thought that if he had a mental health problem it would have been identified and treated after six years in the prison system.
Personally I can't see why he couldn't accept wearing just a pair of speedos in public. That would lead him to be almost entirely free from the constraints of clothing. Why is exposing his genitals in public so important to him?
As for clothing being a social construct! Doesn't it have quite a lot to do with a need to protect ourselves from the weather?