I don't mean "lost" in a literal sense, I meant he lost whatever his intrinsic motivation was to explore the world at the moment he put the game down. There are little things you can do in the game that the game does not push you to do with quest logs or through map markers. So whatever he was doing in the game that was pushing him forward at expense of the things he didn't like about the game at the time, lost its influence. The game is driven by small moments where you think "That looks interesting, I want to go there... I want to see if this works... I want to see what happens if I have these two systems interact. Can I solve this puzzle?". You are not going to have those moments away from the game. For example: If you aren't actually solving a puzzle in a shrine, the only thing tantalizing you is the prospect that finding a shrine is worth it. Solving a puzzle is a different motivator than finding a puzzle location.

I don't think think the issue was just the repetition of the dungeons, but it is a major contributor. I mean he enjoyed games like Destiny and that is a lot of repetition and running the same maps over. I think that something about the gameplay loop in Zelda stopped working for him. But hey, different people have different tolerances for different kind of tasks.