That was the developer's decision and what they say about rebranding is : "The Core Team wanted a name that represented the simplicity and speed of the project, and Nano does just that." I can not say that Nano is better or worst from RaiBlocks, but it is certainly created confusion to some users and some of them are not even sure is this same coin or is it use same wallet. Read more here.

Good news for Ledger Nano S hardware wallet users , one of the Nano Developer is finished application and now is only up to Ledger team to add this app to their store. This will be great move, first light and secure wallet for Nano