Why can't we buy older cosmetics?

I really can't understand Blizzard. They do EVERYTHING they can to make us spend money in the game (I know that is better today, because of all of the backslash), but they don't allow us to buy previous cosmetics.

Okay, if you want to keep some "exclusivity" to first buyers, a year or 6 months cooldown before selling again is fair enough.

Stuff in this game is expensive as hell (at least in my country) and we barely see any wales around here, because people here don't like to pay that much for game itens, but skins always sell well in any game around here.

Guys at Blizzard should really reconsider "what they want to sell" and "what people want to buy". In my opinion, 90% of the store is silly and overpriced.