Because the rate of change has changed itself. Just like the internet existed for many years before it took off and car phones were around in 1946 there is a point in time where the rate-of-change in either the application or the development of something new changes.
That point in time has definitely come for self driving cars, we're not 'close' but we are much closer than we were even 5 years ago, there is legislation on the books permitting self driving cars from participating in regular traffic instead of on private property only, there is special hardware geared towards such systems and so on.
It's an idea whose time has come, now we have a bunch of engineering problems to solve and they're far from simple but I would not at all be surprised if self driving cars are going to be equal partners in traffic 10 years from now.
Lots of hard work between now but I think we'll see self driving cars long before we will see an operational fusion reactor.
Nothing like a large carrot and the feeling that something should be possible to bring out the hounds. if it can be done with present day tech it will be done, if it can't be done with present day tech then we will have a pretty good idea of what the stumbling blocks are and what kind of tech will be required in order to solve them. That's the minimum that will come out of this, possibly a lot of spin-off tech as well for more limited situations.
Nobody involved closely with self driving cars thinks we're anywhere close to a level 5 system. Why do you think we are?