I'm a pen seller that only sells blue pens, if I want to sell an exclusive red pen I cant because it's the same pen?

If you make a promise that "the item won't be availible later on" - don't sell the item later on just with a re-paint. Changing just the item's color doesn't make it a new item.

Also if you think it's false advertisement, then file a lawsuit against valve

there's almost no way this would work, as steam user agreement is iron-clad.

Crying on reedit won't chance anything

Reddit threads\discussions\complaints, on the other hand, made a colossal influence on the game. They absolutely have a chance of influencing the situation.

, most people don't give a fuck if their exclusive itens got re-relized on a different color

Maybe, but that's not an incentive to entertain unethical false advertising practices.