I am wondering if the Garmin Connect or Garmin Dive app, automatically populate the dive site name from the GPS co-ordinates or do you still have to manually enter the site name?
Garmin Connect does not as such but will name the dive based on the approximate location. For example, all my dives default to "Sydney Single-Gas Dive" or "Sydney Multi-Gas Dive" as appropriate. i.e. it knows the dive was in the Sydney area.
I manually rename the dive and the location.
Both true but they could tap into something like the divesites DB as it's an open and accessible dB, or a Garmin maintained dB, the key is that it needs to be able to be locally overridden. I suspect this would be fine for 99% of users, and for most of us we call the divesite whatever the local dive OP tells us. Most people write it down and only look up the name if asked about a specific dive or are thinking of going back.
But your point is valid there would be those that disagreed and it would take time to populate