It's still an improvement if the large place that burns stuff extracts more energy than tons of small places burning stuff. Not to mention, it's easier to then replace the few large places that burn stuff with something cleaner than having to replace every single car on the road again.

There are lot of parts in the network. No one claimed they would all make a step transition overnight. Part of that is to replace parts of the network which continue to work, while being capable moving the other parts forward.