It has nothing to do with the money to renovate them. There's a long and arduous process for the city or any of the various nonprofits doing similar work trying to either rehab abandoned homes or demolish them to build larger buildings or green spaces. Many of them still have owners and you still have to go through the courts accordingly and it takes literal years to do so.

This older, but still incredibly relevant 2016 episode from Planet Money describes the process in detail.