You're not wrong in terms of how much time people can spend on something that doesn't take much thought (it can be a comfort, even), but your diagnosis of the problem is way off. There's nothing about modern video games that can receive the blame for this, even if I hate what gacha and friends have done to the place on the design perspective. (Fortunately there's still plenty of market that's not design I dislike. Another commenter mentioned games as Vegas 2.0, but I don't think that commenter is a gamer either. Casinos are absolutely dominated by the shittiest of games, from a pure game design perspective, with seemingly no room for anything else. The overall gaming market though? It's quite healthy and varied. And even the cancer in mobile gaming is but a harmless mole compared to the tumor of casino electronic 'games'. And to be clear, people can spend/waste their time and money as they choose, that's never been my complaint against any of it, I'd sooner complain about people complaining about others wasting time on X.)

I'm surprised, you seem to have spent enough time around kids (and were a kid once yourself), yet you think "replay value" (which is inflated for some games by not having a definitive end) is at all a modern thing, or even necessarily a bad thing. This extends beyond games. Do you realize how many hours of Frozen have been watched, over, and over, and over? Or how many hours listening to Baby Shark? Or whatever's going around now? Or whatever was going around when you were a kid? (Insert favorite classic Disney movie? Tetris? Cribbage? Chutes and Ladders? Minecraft?) Kids love repetition -- humans in general like repetition a lot. Heard of the Hero's Journey?

Don't underestimate OoT either! If a kid liked OoT enough to reach the end, it's unlikely that they'll just move on immediately unless they're literally forced onto the next shrink-wrapped "brand new" experience by someone. (To be sure, if I'm ever a parent myself, I will consciously do a bit of that pushing to try avoiding letting them repeat the same thing like some popular movie too much, but I'd be a hypocrite and a fool to think I can or should prevent all of it. Besides, it's remarkable how many times you can watch/be all but forced to watch something even as a young teen (cough Napoleon Dynamite) and yet retain almost no memory of the thing's details as an adult.)

OoT is a real-time interactive simulation, such things are naturally just fun to immerse in, even after you've beaten Ganon / "reached the end". But besides just continuing to 'hang out' aimlessly in the game, there's all the stuff they could aim at in order to "100%" the game, or just go back through optional/missed stuff in general/at leisure. (But everyone who plays OoT needs to get the Biggoron's Sword!) So the kid could do that, even talk to friends playing the same game (socializing skills even with a 1p game!) and trade notes or experiences, or compete on times for various races, or they could develop their own random aims, like a quest to smash every pot. Or start a new playthrough but with some difference. Or they might discover the speed running scene and get into that, or just generally see the crazy nonsense people have done to that poor game's code. Again, don't underestimate games like OoT, Super Mario 64, Dark Souls, Megaman X, or Chess, either; having an "end" doesn't protect them from being the object of people's time spending/wasting.