3000 orbital tungsten rods of the UN world police.

Whose jobs are going to be available when the population of people in elderly care doubles while the working population decreases?

Yes. And because it takes years to figure out the science part. The industry that produces the rest of the spacecraft is set up to also work on year long timelines. Producing the thrusters for a satellite in a few weeks would just be a waste of resources. You would spend most of the year without a job.

It is possible to do things faster. If things are truly desperate I am sure the US military's would just snatch up every satellite engineer they can get ahold of and give them blanket checks to whatever they need to manufacture a probe as soon as possible. But probes require a lot of highly specific components. And if only one of them is missing the entire program grinds to a halt.

Designing interplanetary probes takes years. You could probably speed that up in an emergency. But there are no manufacturer out there that are prepared to build probes rapidly.

Then you need to travel to the asteroid, and you want to hit it years in advance of the impact. Adding all that up you probably need something like 5-10 years of early warning. Depending on how devastating the impact would be.

If you want to be serous about planetary defense you should have one of these probes ready in advance in case we ever need it. A new falcon 9 rocket is launched every week. There would be no problem swapping out a payload in the event of a emergency. You could launch the probe in a matter of weeks instead of years.

>China produces the most amount of coal emissions globally

And they also produce the most amount of new renewable energy globally.

Turns out that when you are the biggest country in the world. You end up winning a lot of "Most amount" statistics.