In theory, TfL could sell its land to the highest bidding developer and turn a blind eye while yet more luxury flats are built for investors benefit. If we had a Tory mayor, that may well have been the preferred approach.
Or TfL can try to maintain some degree of control over the development to try to secure affordable homes. This will likely secure less revenue for TfL but you can see why there is a desire to take that approach when safe, secure homes are so unaffordable for so many.