Public L1s/L2s don't really provide the agency TradFi requires at the execution end.
So instead, they would rather use public blockchains for settlement, while keeping execution on a rollup they control—run in a highly centralized environment.
This allows them to offer a neobanking experience to their existing user base, rather than risk losing them to other L1s or L2s, where token price is often closely tied to the quality of UX.