I can't speak for cargo skins specifically, but when some "asset" sells for an abnormally high price, there is usually something else going on. It's like when a condo which would normally be worth 200k sells for 380k, it can be a way to turn dirty money into a "reasonable" sale. Sure the seller has to pay taxes and such on it, but if there's no strict know-your-customer requirement, you can accept money from any source.

The usual arrangement is that the seller inflates their price a lot, and then the seller provides the product plus a kickback to the person who wants to launder the money. Now the launderer has a real, valid asset, plus optionally some of the overpaid amount in cash. As long as the buyer reports the income and pays taxes, now the seller has laundered the money. I am oversimplifying somewhat, but that's the idea.

A lot of properties have been sold by a certain high profile American politician that way in the last decade. That's a fascinating place to start studying the scheme.

CSGO skins and steam keys work in similar ways, the scheme generally looks like this (or atleast it used to, haven't looked in a few years).

1. Buy/ obtain stolen credit card details.

2. Buy CSGO skins / Purchase steam game as a gift with stolen CC.

3. Sell skins/ game keys through a 3rd party, online marketplace.

4. Collect profits.

Congratulation, you've converted dirty money (used to buy stolen CCs) and potentially dirty money (charges put on stolen CCs) in clean, washed money!

Of course you can do this scheme without the stolen CCs (just buy steam games/ skins) but the CCs have a nice multiplicative effect and they add more obfuscation.