LookML dashboards can only live in the LookML dashboard folder. There is this product feedback to allow functionality to move them out of the LookML dashboard folder so that they can live in other folders.
As a workaround, when viewing a LookML dashboard, we can click “Copy from LookML into a folder” (documentation) from the gear menu. This will make a UDD copy of that dashboard in the folder we choose.
Looker just released a new feature that allows you to move LookML dashboards into other folders. Once you push the code to the master branch and is live in prod, make sure you are not in dev mode and where you are when you select the 3 dots next to the LookML dashboard you now have the option to import and move.