Expired Tokens

So I'm just curious why tokens are made to expire after a certain time? I'll be honest, I've had them done since the beginning of august and I should have used them however I'm quite indecisive regarding a lot of things and I'm a compulsive hoarder.

I'm all for missions expiring until a point of time as it should be limited to people who actually play during the event however I don't believe that our tokens should be just be removed as that's just a let down. Is it due to the options that we can spend tokens on that it becomes somewhat unfair if prices change in the store for a specific emote/icon? I'm just looking for clarification, as I traveled and came back 1 day too late.