There shouldn't have been a need to merge
It's weird there were two different OSes to begin with. I suspect that Google like most large companies ended up with two in-house teams with similar but incompatible ideas for low cost devices and didn't have the guts to strategically pick one over the other.
Android is great for tablets but its mouse and keyboard support can be generously described as perfunctory. If Google had concentrated on fixing that and putting in a desktop mode then there wouldn't have been a need for ChromeOS. Android would have served both purposes.