LOL, that's such a wrong take I'm surprised it got so many upvotes. Google didn't forget anything.
1. If Google would have forced their own apps on all manufacturers then they would have been 100% hit by antitrust regulators over this obvious breach, plus manufacturers might not have went the Android route back then, so leaving some room for the manufacturers, went a along way to encourage everyone to trust Google and go on board the Android train, instead of feeling they'll be Google's hardware lapdogs
2. Google is already protected enough by forcing Play services on all Android devices thereby getting a cut on all playstore purchases and ad targeting.
They're not stupid. Google is exactly where they wanted to be.