cards do stuff.. you just need to unlock prestige.
Most of my cards work, already (and they show up in the tooltips as "Cards" for the effect). Just not the one I mentioned. Now, if cards are ONLY supposed to work when activated during a prestige (which basically means you're going to wait WEEKS before you can use a single one since you can only prestige duplicates) then their values are WAY too low. Pointless to get something like 1.25x capacity for a single prestige with that huge of a delay between getting to use them.