Google has a fundamental problem with perception of which roads are equivalent.
It often sees rural 60mph roads as equivalent to highways where in reality they former are narrow, bendy, sometimes dangerous, and you can never so more than 30mph on them safely.
When I drive, I want the less hassle. I want to get from A to B with the least amount of thinking and stress. I would choose the road I know, or the road with the least number of turns over a road with even a 10-minute saving any time.
That's why I always turn down Google re-route suggestions. They are absolutely silly and detached from reality, and it annoys me to no extent that there is no global setting that aould allow you to disable automatic rerouting completely.
I'd like to be able to start the nav, look up the route, correct as need it and pin it so that it doesn't change mid way. Any modifications to the route should only be made on demand when I interact with the maps and tell it to try and re-route.
There's also something else that irks me considerably on Google Maps. In the UK it is illegal to interact with your phone in any way while driving. When Google re-routing pop-up appears, the default action after the timeout is "accept". This means that if I wanted to just follow the route I chose at the start of the journey, I'd have to break the law to turn the suggestion down.