Why couldn't they have just used the same name, and upgrade the software?
Why was there this horribly confusing announcement with EOL dates only 6 months in the future?
Because they had an online service/web app (Drive), a mobile app (also called Drive) and a desktop app (also called Drive) which were related but all had different features, and now the web and mobile apps keep the name, but they have an organizational desktop app (File Stream) and a personal desktop app (Backup and Sync) that are distinct. Sure, one or both of the two desktop apps could have kept the Drive name, but that actually would have been more confused.