[2020] Fountain requires road traffic? Why?

It depends a little on the building itself, but it sounds like one that is meant to require a road nearby. To have it working fine, you will need a road within 2 tiles of the front of the building. If you want to use an invisible road, you will need to subscribe to one on the workshop. Like this one for example: https://steamcommunity.com/sharedfiles/filedetails/?id=1229443937&searchtext=invisible+road