Earlier quoted context omitted.
It's one more step along Google's path to eating the internet. Google-served content discovered through Google search rendered in Google's browser running on Google's operating system on a Google-manufactured device connected through Google's ISP and Google's network protocol (QUIC). Vertical integration.
You know the cool thing about this integration ? Any part can be replaced. Some instantly, some take more time because they involve physical stuff. People use the Google integration because it's there by default, not because they are locked-in.
While yes, you can install CyanogenMod (without Google Play Services), or others along those lines that remove the "Google" out of Android, it's true value (for most common users) is Google Play Services.
While you can say that you can get apps from apkmirror or F Droid, most apps still won't work without Play Services (case & point - Snapchat)
my entire point being - yes, it's very easy to have alternatives (and their importance can't be ignored), Google services (be it Play, or Gmail or others) are what people are looking for.