I suspect that it was never intended to be a port of Link to the Past.
I bet early in development they just tried to copy over the map from it to help them test things. Test the basic systems, test the artwork...
Trying to copy the map from LttP would be a good way to figure out what tiles you need, and how you need to adjust the art style to fit the restrictions of the console. It gives a good concrete goal: can I copy this design into this tighter space?
Plus running around trying to play a map like that is great way to really push the game design into some realistic scenarios. You can get a good feel for how different uses of space works and doesn't, how various enemy designs work and do not. There is a great value in copying over a map like that; it's a lot easier to really run a game through its paces using a map that looks/plays like a complete one, rather than a bland empty field.
Porting over a game that is still selling on store shelves though? I don't see an advantage to that. I would sooner believe that early in development they were planning on this being a direct sequel to LttP than a direct port.