Rebuilds

I saw some railfans on youtube post about the f40ph-4c unit at ss a few months back & I don't get it. Why focus on rebuilding current equipment when it's possibly not going to be needed in the future? Lots of other units are being rebuilt as well. The 3cs are pretty new & reliable bc of that. Are we really digging ourselves into using this equipment when we're actively looking at other equipment for rr? I get it's going to take time but why do this when we could at least keep the 3cs around as is. The geeps definitely needed a rebuild no doubt. Am I missing something here? Leases cost $. Could that be used for more pressing needs or rr?