The exemption for non-public generators is there for a reason too.

There are lots of businesses and homes with onsite generation for various reasons, and most of them run for less than 100 hours per year. Not a lot of reason to add a reporting requirement and a strong emissions requirement.

Focusing on large scale generation was a good choice (that has worked for decades).

In an ideal world, congress would see this and adapt the rules to apply here as well. Probably an hour limit or a capacity limit or some combination would be a better discriminator than for public use.