Because the cost would be high, and there would be no quick way to undo it if it turned out to be a bad idea.
And because in the real world you're not allowed to just say "other than all the environmental damage, why not?".
And because in the real world you're not allowed to just say "other than all the environmental damage, why not?".
“Other than all the environmental damage, why not?” all the time. They weigh the likelihood of being caught or not, and do a cost/benefit analysis. They choose environmental damage just for a 1% increase in profit margins.
If they can do it, why can’t a properly funded radical geoengineering activist group do it?