Presumably because those funds are being used for welfare. Let's imagine my country does just that. Let's take half of the federal Canadian Social Transfer to the provinces and spend it on something climate-y. Great.

Politically, I do not believe that the hundreds of thousands of disabled and elderly people who would find themselves starving on the streets, would be popular. Chances are it would backfire. Why cut the incomes of the poorest in the wealthy world, rather than the wealthiest in the wealthy world? $1000 means far less to me than it does to someone with an income of 1/20th of what I have.