I had a feeling that this was related to body hair and googled "Bubba top button", sure enough:
“I didn’t like how my chest hair stuck out from the top of my shirts, so I started buttoning them all the way up to the top. Now, everybody recognises me as the guy who buttons his shirts to the top, so it’s just something I do naturally.” - Bubba
It's born from insecurity when he was a teenager and just kept going from there. Now he's stuck with it, if he got caught unbuttoned it would be a social media meltdown.
Men are supposed to be hairy.