when it was release, it was actually introduced (internally) as something like, "what would email look like if were invented today?"
I can't really pinpoint any one thing. There really was a mass of mistakes that all lead to this imploding heavily. I seem to recall that the fate of GWT was intertwined heavily with it. Very heavyweight widgets to support the general idea of massive collaboration in real time.
I suspect the killer is that "real time" portion. People love to talk about that. Few actually want it. (Fewer still need it.)
Real time is good for collaboration but it sucks for messaging. A good messaging platform allows you to ignore it until you are ready for it.
Since these platforms need to capture an entire network of people at the same time if there is something preventing someone from bringing all their friends/collegues in at the same time then it is doomed to fail.
I think they've learned the lesson by now at least, since their latest communication systems (Duo and Allo) had open signups. If those two fail it'll be because they were pointless (from a user perspective) entries into a crowded market of established players who already had network effect lock-in working them.
The impression seemed to be that they would kill buzz/reader/wave, and the folks would just naturally turn to what they then offered. The reality seemed as much that many of us were unwilling to try anything else from them until it was clear it was good and going to stick around.
