Maybe games like Fortnite have made this a news to some? But choosing your PvP shooter outfit for camouflage benefit has seemed to be common knowledge for decades (even if some people chose style over function).
If this were a skin available for free with the game I doubt we'd see this angle
There's a disgusting incentive structure here
Company releases DLC skin for $10 that provides competitive advantage to the most unsporting players, altering the game balance in a way that leads to many frustrating and unexpected games for their players, who have to swallow their pride and pull out their wallet to keep the playing field level. Company makes a lot of money.
That's why.
... and then they still buy the next "overpowered" skin that comes along.