Don't be so sure about "obviously" when they start talking about "water vapor emissions"...
It uses the term “greenhouse gas” to refer to CO2 and uses the term “air pollution” to refer to what people traditionally think of as air pollution. For example, in one place of says: “Consequences of CO2 enrichment and climate change for natural terrestrial ecosystems could be modified by other environmental factors, both natural and man induced (e.g., by air pollution).” So that’s treating “CO2 enrichment” (emissions) as distinct from “air pollution.”
Society uses labels to group things together so that we can treat similar things similarly for various purposes. For example, when we talk about “education” we usually mean teaching kids in schools or colleges. Of course, there’s lots of other things you can call “education.” But if the Department of Education comes in and says it’s going to regulate technical presentations at software conferences because that’s also “education,” then you’d say: “that’s not what people mean by the word education in this context.” That is, we have a consensus about what “education” encompasses and what it doesn’t for purposes of government regulation, and seminars at conferences falls outside that understanding.
Because society uses labels to delineate the boundaries between different legal regimes and sources of authority, and adhering to those boundaries is important. The FCC (Federal Communications Commission) can't point to the traffic on a fiber cable within a data center and say it falls within their jurisdiction because that's also "communications."
It's especially important in this context, because the half-century-old laws and regulations designed to control soot emissions from factory smokestacks is ill-suited to managing CO2 emissions. The fundamental premise of the Clean Air Act is that pollution can be controlled at the source with control technologies (RACT, BACT, etc.).
This focus on control technologies puts well-defined guardrails on the EPA. The EPA can't go around making big decisions about how factories work or what people produce. They can simply tell you to put the best reasonably available scrubbers on your factory. That approach completely breaks down when it comes to CO2, because there is no such thing as a "CO2 scrubber." Treating CO2 as a pollutant puts the EPA into a role of supervising the energy sector that the agency simply was never designed to do.