Why does swapping in L2 cost so much more than mainnet (L1)?

I was under the impression that swapping coins in L2 should be cheaper, but instead it cost more than 3 times.Swapping in L2 (Arbitrum) for 5 Eth into USDC costs $22.37Swapping in mainnet for 5 Eth into USDC costs $6.73L2 Arbitrum swapping 5 Eth to USDCMainnet swapping 5 Eth to USDC via /r/ethereum https://ift.tt/EpB2cvg