The Sims Studio want so much to make easy the Green Eco Footprint that it becomes impossible to keep the Industrial Eco Footprint in a neighborhood no matter how many generators and fireplaces are active.
4 days to decrease but 1 day to go back to Neutral Eco footprint.
The only way is to apply the cheat code every day.
An Industrial lot trait is also missing to prevent it.
For example, Industrial Eco Footprint : 9 but it's positively Green.