(1) https://www.theregister.co.uk/2017/12/22/grsecurity_defamati...
1. They're a surveillance company that has more actual and potential earnings the more they know about their customers. They get good margins when their customers lack privacy with devices locked into Google by default.
2. They don't care about users' safety since make billions off Android platform but wont even patch vulnerabilities quickly. They have enough money to design a server UNIX from scratch plus a full-custom CPU plus mitigations from code injection at CPU level with all that leaving them with a few billion in revenue left out of Android alone. They just don't care since they're a public company about squeezing out every ounce of profit.
So, their incentives ensure they will leave the devices insecure. Someone will have to make their own versions that are secure like Copperhead and separation kernels before them (eg OK Labs) did. Alternatively, convince Google to offer a paid, secure option for their own internal use if nothing else with them recovering costs by eating up the cryptophone market's revenues.
So, Google securing Android would cost them a lot of money for fixing the customers' problems that dont affect Google. Then, it might cost them piles of money later in lost ad revenue when now-private services make customers black boxes of sorts.
I think there's a lot of middle ground to explore but surveillance or public companies don't usually go for it. Offering a paid, surveillance-off version of each ad service is one of those. You will rarely see that as simple as it is to do.
Personally I use CopperheadOS as my daily driver because it stays continually ahead of Google (and groups like AOKP, LineageOS etc) in terms of Android hardening. It goes well beyond just not having Google Play services.
See their details on their approach and design: https://copperhead.co/android/docs/technical_overview
They make continued patches to Android as part of a security and privacy first approach. Many of their patches get upstreamed by google months later (if at all) but CopperheadOS users get them right away.
Google has their engineering efforts focused mostly on new features and compatibility. They are happy to let firms like CopperheadOS be further ahead in security research and take their patches where it does not break compatibility.
It really depends on what you want to optimize for. Security/privacy or being able to run all the latest games and social media apps and the consequences that come with them.