Because global warming leads to climate chaos, not just nice hot summers. The world is, on average, much hotter than it has ever been but within that there is a lot of unpredictable variation. For one thing, weather fronts are slowing down, so a hot spell like most of Europe are having, or a cold spell like the UK are having would last for a couple of days and move on. Now they’re getting stuck, which means it hangs around a long time.
It looks like the Gulf Stream may stop or even reverse, and that will bring much colder weather even with a higher global temp - places like Labrador, which is at the same latitude as the uk - are under snow sixth months of the year.
The idea that global warming = nice summers is incredibly naive.