You should do 2 things for your players.
1. Have an explanation of why when they talk to any of the Arena people.
2. Provide a mechanism to trade any number of other area tokens into Arena tokens. Perhaps only when all else is done with those tokens, i.e. certain tokens have no use once you get everything you can from them while other tokens, like fishing, are usable forever. So some can become Arena ones and some can't.
Please do something like that for your players. Not me of course, I have everything.