That's an interesting and valid question.
As some of us are spending our hard earned cash on these deals, which include arena Coins, why should we not be able to use them and lose out?
Because we have updated our arena fully and been around longer why should we miss out?
The drop rates and items are fairly crap anyway so I don't think it will make much difference apart from to give those of us with thousands of unused coins... Some paid for with cash, the opportunity to spend them.
Also new players could choose to use these instead of upgrading if there is a deal on they are interested in and they don't have tokens.