Hangouts used to be a single product that combined video, voice, direct, and group chats. It was quite good, especially with Google Voice layered in.

Google split that in to Meet (video/voice) and Chat (direct/group) in a half-hearted effort to compete with Slack and Microsoft Teams. You could also say they split it further via Google Voice, which became a standalone paid offering.

The issue is they still haven't solved for external chat in Hangouts Chat, which is a critical feature many rely on in legacy Hangouts, so that feature keeps the legacy version running I think.

They really botched the launch of Google Chat. The original deprecation timeline for legacy Hangouts was something like last June.