They don't block 100% of sounds, far from it. They block rhythmical noises. So if a piece of metal would come off and scrape the road surface - I wouldn't hear it. But police sirens would be audible.

There are luxury cars than come with Bose's ANC built-in. They'd have the same problem if there was one.

Finally, I never use it in a city, just out on a long drives, where road surface is more ruff and listening a podcast via car system is more difficult than useful.

Deaf people don't need extra training before getting their license in most countries.

This also applies to the radio. I typically have my radio cranked up. Any time I turn it off, I'm astonished at the noises my car is making. It always occurs to me that I would probably notice mechanical problems earlier if I was used to just listening to the car so I could detect changes in what it sounds like. Then I say, "screw that" and crank the tunes back up.