Some cards never leave the "biggest increase" or "biggest decrease" list.

I have cards that haven't moved off the "biggest increase" and "biggest decrease" options, for 2 years now, when searching through my collection. Meanwhile the price stays the same. Meaning there's a green or red arrow next to a listed value which never changes. If a card value hasn't changed in years, why would it show an arrow showing change. There needs to be a set amount of time a card has an arrow.. A month or so max. Unless that card continues to move in the market.