Nobody is talking about stated reasons, the question is what grounds Google would have to object on if they chose to. That means it's speculation.

Edit: I'm no longer trusting my memory lol. Apparently security was why LOS didn't integrate it (see https://news.ycombinator.com/item?id=31171788). I'm still leaving my original reply below.

The SafetyNet part is something I read from somewhere else, though unfortunately I don't remember if that was LOS or some random developer on reddit/XDA. You can treat most of this as (oft-repeated) speculation by users.