Everything in a car has to be certified for safety. Infotainment systems integrate deeply with cars - they consume and expose a lot of information that isn't guaranteed to be expressed over standard protocols, and most of them aren't even in consistent sizes or shapes.
Yet I can buy a double DIN head unit running android auto and just whack it in my 2012 corolla.
I think the major problems here aren't safety or engineering, they are purely economic.
There is a difference between can and should. Third party entertainment systems should not be a problem. In reality they are because of bad designs.