Because Jesus did not like the idea of a Holy place being used for base commerce, and specifically for charging exorbitant currency conversion rates, as well as exorbitant rates for various animals such as doves, which were ritually sacrificed to atone for various sins.
The merchants in the outer court were… basically specifically permitted to operate there, authorized by the Pharisees, who in turn took their own cut.
Its… kind of similar to the rejection of indulgences during the later Protestant Reformation.
If you can only be free of sin or ritually cleansed by rituals that require fairly pricey things… and you are too poor to afford what is required for you to undergo that ritual, then you are basically paywalling your spirtual cleanliness, too poor to become right with God.
… The Bush era joke is still holding up:
Americans learn geography via which countries they (threaten to) invade.
… I guess it is just fully beyond a joke and is now just completely literally true.