Ah so you are not talking about the source code, but the anti-abuse features.
It is important to understand that this is not Google pushing stuff, but addressing developer demand. That is, the choice is not "Either Google provides SafetyNet or apps don't do anything," it is "Either SafetyNet or apps instead use other 3p solutions that are more fragile and problematic." In fact growing use of 3p solutions has made Android dev problematic as they break with each new platform version.
@yacc143
By and large I don't think Google uses SafetyNet for its own apps, because it isn't seen as so necessary... except for stuff like contactless payments. And there is no way you would have contactless payments without device integrity verification.
I also find it frustrating how much app developers feel the need to protect themselves from the platform with this stuff, but I don't see how to generally convince them otherwise. (And Apple's Android security FUD doesn't help.)