"Our environmental footprint has many facets. It isn’t just the code, but how the community maintains and extends the code. Every line of code takes energy to execute, energy to write, and likely represents a combination of communications efforts to nail down."
Drupal drives about 2% of the web. The internet is responsible for about 2% of global CO2 emissions. Reducing the page weight of Drupal Core will eventually reduce the impact of over a million sites. It is a tiny step in the total reductions that are needed, but at this stage, all efforts help.