This seems like the biggest failure point. Humans are basically unable to prepare for major but rare events (eg the pandemic response). Day to day politicing always wins, and when the problem is suddenly on top of us we've got nothing.

I think the best we can hope for (apart from not having an asteroid heading our way at all) is that we'll have sufficient notice that something can be done. If we had a couple of years notice, there's a reasonable chance the deadline would be motivation enough to get something built.