Why can’t I directly buy tokens on L2 on CEXs right now?

For example, a pretty straightforward flow would be: Alice transfers her ETH on Base into a Base wallet managed by Coinbase. When Alice wants to trade ETH -> USDC, Coinbase can match Alice with another order of USDC -> ETH also on Base and facilitate the trade just like it does for L1. Alice now can transfer her Base USDC out of Coinbase into her own wallet and avoid the network fees of L1 (besides calldata fees).

If we can trust the sequencer, doesnt this process have less latency and cheaper fees as the same L1 trade? What am I missing here? Or are there legal concern that I am blind to?