Graph below shows the transaction fees collected from all transaction on Terra. We can see that most popular currency used for fees are $UST, $LUNA and $KRW. We also can see that the sum of fees collected correlates with transaction volume.

Graph below shows the fees collected from native swap (Market swap on Terra Station) and other type of transaction. We can see that swap fees from native swaps is very miniscule compared to other transactions.

How does Terra pay the $LUNA stakers.

So, you might be wondering where the yield that are paying stakers come from. Transaction fees or known also as Gas fee is the small fees that covers the cost of processing a transaction. Any transaction that does not contain enough gas will not proceed and transaction will fail.

Every block, gas fees are sent to the reward pool and dispersed to validators who distribute them to delegators in the form of staking rewards.

(according to Terra Docs)

In conclusion, gas/transaction fees are used to pay for the transaction and the transaction fees will then be distributed to validators. The validators will distribute the rewards to delegators.