Hopefully the AA devs can understand that.
Devs don't decide these things. It's management with their business decisions.
Google has sunk millions (10's of millions++ really) of dollars into creating a special app environment and APIs for Android Auto. They have a team that approves AA apps for non-distractibilty and they have specialists in car UIs and lawyers a plenty advising them about all this.
IMO they are not about to turn around and say "Screw all that, we'll just let all notifications through".
They (and Apple) have been working on this for years and we've been wanting it for longer. Finally, it's STARTING to get close to being "real". And still there are problems.
Google and Apple are arguing with car manufacturers over liability. Technical problems are going to cause some "AA compatible" cars to be released this summer/fall without the AA HU part working properly yet (Already happened.)