It is not at all obvious that trying to develop new revenue-generating opportunities will actually bring in more revenue long term compared to optimising and improving existing revenue generating sources. And it's not like the old code stops working once you start reworking it. Give your engineers N months to rework the old code, and if it's not better you don't have to deploy it.

Every larger company I've worked at had enough engineering overhead that they could afford to have small teams working on both reworking old stuff and creating new stuff, while the main teams kept the working stuff generating revenue.