Block where ~20 rowhomes were replaced by 6 detached homes in 2013
The block is in Garfield. Going through historical imagery on Google Earth, you can observe that the original rowhomes gradually fell into a state of disrepair and were demolished one by one over the 90s and 2000s until the land was eventually redeveloped in 2013. At least one of the reasons they weren't redeveloped into a denser configuration more similar to the block's historical development is it would have been illegal under the land's modern zoning. For example, despite formerly containing rowhomes the land is currently zoned for 5ft minimum side setbacks, meaning a 10ft minimum distance between buildings.
This is just one example of a phenomenon that has occurred a number of other places around Pittsburgh over the decades, especially in the Hill District.