Unfortunately, whichever is the reason, the result is the same: anyone without a Pixel device can't use it at all and anyone without a very recent Pixel device will find themselves much more limited. I'm not blaming Graphene, I'm just saying I can't recommend it to people who... don't have a Pixel... Which, unfortunately, means a *huge* number of Android users.
And no, we don't all have hundreds for new devices. (Don't forget also, we have to work with the sellers and etc — especially when buying used — to ensure Verizon hasn't gotten their dirty claws on it and locked it. Yes, Google lets Verizon lock them. Not sure if any others do.) Buying used comes with its own caveats and still isn't exactly cheap.