This is a good point that I did not consider - I personally don't do a lot of city driving (I do but only for "pleasure" - I don't work in the city, so I'm not on a time crunch heading there), so it is extremely rare that there's something that causes me to need to re-route when I'm on my way to work or wherever.Most of us drive with no assistance from our phones or GPS. A trip you take day after day, you don't program into your phone. Then as you're driving, you start to see delays. If you're a listener to a station with frequent traffic reports, you'd know the problem before you run into it.
If it's someplace you rarely go, you might program Waze or Google Maps before you start driving. But human nature is not going to have you do it with a frequent route.
Maybe someday, you can ask your device why you are hitting traffic and it will know an alternate route. But that's not today, not if you didn't program your route ahead of time. And once you see delays ahead, you SHOULDN'T be fumbling with your device while driving.
That said... when I'm with people who have Apple CarPlay, if they're on their usual commute, their phone will automatically suggest routes. Mine does this - it knows when I'm heading to work and around 5 minutes before I leave, a notification comes up saying "Take *this road* to *this location*. Traffic is light." Unless something happens while I'm already on the way, I'd likely know about it from my phone. So there's that, too.