Don't you get to flip kingdom cards at the end of a season to use their powers again?
No. You flip Master Craftsman cards to use their powers again. But Kingdom Cards are Immediate (one-time use triggered on taking the card), Permanent (passive power for the rest of the game), or End (endgame money).
The only exception is Hoarder, which lets you flip (tap) the card once in the whole game to take a Kingdom Card at the end of a turn.