It's really not. It's not like the cooling effects of molecules like sulfur dioxide et al haven't been studied after all....
The average atmospheric lifetime of sulfur dioxide is about 10 days.
The average atmospheric lifetime of carbon dioxide is at least several centuries, probably a lot longer. It's not actually that well understood because of the way the ocean is constantly absorbing (and releasing) atmospheric CO2. Ocean acidification, by the way, also a big deal.
If sulfur dioxide, or any readily available molecule for that matter, could feasibly be released into the atmosphere to reverse warming without risking even more adverse consequences, then the scientific community wouldn't be jumping up and down about how big a fucking problem anthropogenic global warming actually is.