In order to reduce calldata usage (and thus, gas), StarkEX does not publish all the on-chain transactions made, but rather just the balance changes. For example, if Alice transferred Bob 500 USDC, and then got from Charlie 200 USDC, we will only publish Alice's new vault, with a minus of 300USDC, compared to the previous state.
This optimization is very efficient for real-life scenarios when heavy market makers make a large portion of the transactions, using only several vaults.