My point wasn't exactly that they had no choice, so much as it was a choice they quite understandably weren't going to make.
The AT&T analogy is kind of weak here because they weren't operating in the same business environment. AT&T was doing it in a B2C context, Google's Android business at the time was 100% B2B. It's easier to take this kind of risk as a major telecom operating in a B2C context, because consumers, as a body, aren't going to punish you that badly. Case in point was that, while these Android phones sold poorly, it hasn't actually tanked AT&T's business.
Whereas, if Google had sent Samsung, LG, Huawei, etc over to WebOS or wherever, the impact to Google's Android business would have been large and permanent.