They needed to rewrite their Windows version from scratch multiple times and their first major release from this rewrite marathon was 1 Password 6 which had no support for local vaults.
This looked like a clear deprecation of their local vault support but their Mac and Android versions never dropped support for those. I don't know if AgileBits ever planned to drop that from the other versions but after some vocal feedback from their users they stated that local vaults will remain.
The upcoming 1 Password 7 is the first release after the rewrite to support local vaults again on Windows. (BTW, their previous Version 4 for Windows with local vaults was still supported during the 1 Password 6 timeline. Afair, they stopped to sell stand alone licences for those after a while.)
They lost me over this issue too. It felt like they only decided to support local vaults again because there were so many complaints from loyal users about the deprecation, which makes me think at some point they may try to end-of-life it again. I wouldn't mind paying for a new license every few years, but I don't want anything on their cloud.
1Password 7 re-adds local vault support to Windows for standalone license users at the very least. Not sure about subscription users... as there seems to be conflicting information about this.