Who knows? Let's say they wanted to do some shady shit, is writing an email(with the possibility of discovery) on that, is the only way to go about it?
I'm probably more cynical than most, but I'm willing to allow that they seriously wanted to just get into security cameras quickly. It probably started "innocently" as that, but then once the deal was done, the others in the org could start seeing how to use things to their advantage.
I was even thinking it would help their "alexa, open the door for UPS" home system as their point. Again, giving them the "good idea" initial thoughts before someone else took elsewhere.
I really don't know why I'm being so generous to AMZN today
No, but we've seen that even high ranking executives who really should know better really often do that.
I would expect at least something that hints at it, e.g. the absence of another good reason, a hint at other reasons, "synergies with" mentioned etc.
Of course, as you mentioned, there could still be such motives, but with this trending on HN I expected some bombshell where they more or less obviously state that, not such a mundane assessment.