Most of the really good players I knew couldn't care less about skins. People that did suck bought skins to feel better about themselves ("yeah, you won, but I have a $20 Udyr skin, noob!") Except one guy which was pretty good but had a gambling problem and liked the random aspect of buying chests.

What you describe is probably the social dynamics in your son's group of friends, which are probably kids and mostly suck, which makes buying skins the social signaling of their worth, for lack of a better metric.

It's essentially the digital version of the fashion industry, which most people seem to viscerally understand-- aesthetics are the primary motivator for most people's clothing choices, and they are willing to pay a significant premium for some items on this basis.