I remember reading somewhere that they did not integrate to not alienate other phone manufacturers, they were trying to avoid making the manufacturers feel like second class citizens.
It did. The have a majority of the market. They don't make money selling phones. They make money selling ads. As long as all the phones are using google search and ads they do well.
Simply put so that the oems like Samsung were not allienated into forking Android or going with another OS not that Samsung and Lg didn't try going with another OS.
Presumably to avoid any impression of special collaboration between Google and Motorola that would have spooked the large Android OEMs of the time - Samsung, HTC and LG.