I was a developer on both Lotus Notes and Groove, and I think both died for different reasons.
Notes was replaced by the web (and Outlook). Notes was, IMHO, ahead of its time. It was one of the first client-server systems where the client was treated as a full peer in the network. You could work offline for as long as you wanted and then the client would automatically synchronize with the server. It had military-grade encryption, a built-in development environment, integrated full-text search, and programmable agents for scheduled data processing, alerting, etc.
But the web was much cheaper and benefited from network scaling laws (the more sites, the more value it accrued). The web is a perfect example of "worse is better". The complexity of Lotus Notes kept the price high (both financially and in terms of time-commitment).
For Groove we doubled-down on peer-to-peer synchronization. Notes had synchronization at the "note" level. If two people edited the same note while offline then there were conflicts that had to be resolved manually. In contrast, Groove had custom synchronization systems for different kinds of data. For text files we could synchronize at the character level. Other data structures could synchronize at whatever level was appropriate.
We used a change-log merge system, not too different from block chain.
The problem with Groove was that the advantages (offline editing) never compensated for the disadvantages (lower performance, lack of visibility in sync state, and difficulty in onboarding).
The use cases that really needed Groove were rare, and not enough to build a viable business.