It's because today, doing anything beyond the most rudimentary and lip-service of net zero is wealth and value destruction and we live in a world where value creation in the short-and-medium-term is all that necessarily matters (e.g. shareholder capitalism). Thus, regulation is necessary.
Edit to add, I know you get it, but for the granola types who don't have a business background, the theory undergirding all this is in our system:
A company merely exists to create value for shareholders by investing in projects that generate cash flow growth and/or return on invested capital (ROIC).
If the ROIC is less than the cost of capital, the growth destroys the value.
Climate Change implementation to processes (did you know that it is widely understood that 7 industries make up 85% of the direct greenhouse gas emissions) is costly and hard and distracts from or actively destroys value creation.