Because the climate crisis is missing one of the key ingredients of a proper crisis: there's never a reckoning time that forces the decision makers to the table, and forces all other things off the agenda.
If there was an asteroid coming, there would be some deadline imposed by the astronomical observations.
If it's a pandemic, there's a time when all the politicians have to stop thinking about Brexit and start thinking about lockdowns.
In economic crises there's that Lehman moment when the government needs to decide right then and there what to do about the economy.
In pure political crises, there's a vote of no confidence in the government and the politicians have to think about how to form a new one immediately.
With the climate, there's just never a time when you absolutely have to do something. People have even tried saying "we have to do something by x date" but you can't manufacture a crisis point, in fact those kinds of deadlines seem to have the opposite effect to what was intended. That slowly boiling frog analogy is somehow quite appropriate.
I think part of it is the nature of noise. Once you see an asteroid, you don't doubt that it's there. Government falls, you need a new one. People get sick in large numbers, better not let it grow.
But if it rains a lot or gets hot, that will pass. Once it passes we're relieved and we go back to normal. Even if storms get bigger and more frequent, the day after is sunny.
My last point goes back to the first: a proper crisis forces everything else out of your attention. 9/11, Lehman, Pandemic, those were all things that blocked out the news. That has never happened with the climate. When did you ever have a news day where all they talked about was climate? Where all the talking heads on TV were climate scientists/commentators/lobbyists? Where you could see politicians going from meeting to meeting with only one topic being asked of them?