One of the most important aspects of Classic Zelda were the maps and the exploration.
You get the idea. Each Zelda game offered you many days of exploration. Ocarina of Time was characterized as ‘you can do anything in this world’!
When GTA 3 came out, analysts treated it as a novel thing. But as we know, video games perform jobs. The job that GTA 3+ was doing was done earlier. If people wanted the job GTA did, they would play Ocarina of Time during the Fifth Generation. With the Fourth Generation, they would play LTTP or another adventure/RPG game. With the Third Generation, it was definitely Zelda. There weren’t many games that allowed you to roam around in a non-linear way.
Ever since Zelda has been transformed to be about ‘story’ and ‘puzzles’, the value of the Zelda product has fallen sharply. No one talks about the vibrant world of Skyward Sword or Twilight Princess or Spirit Tracks or Wind Waker.
I don’t see any reason why Zelda cannot be getting GTA or Skyrim level sales today.