"why dead? - Google Wave was discontinued because there just weren’t enough active users. The IP was later transferred to Apache when the development was discontinued."
Kinda. But more accurately, there weren't enough active users because Google __completely__ botched the beta. In restricting the invites then prevented already establish groups for trying it. For example, if you have a group of 4 or 5 and not as many invites, it was no go.
Keep in mind, Wave was pre-Slack. The market was there. It was primed. It was waiting for something smart and collaborative. Yet Google did the one thing you don't want to do with a team-centric tool...intentionally leave out at least one team member.