Pokemon is probably the best candidate for this, and even though I've spent a lot of time on Zelda games as well, I'm pretty certain that my total playtime for all the Pokemon games I've played, add up to waay more than I've ever spent on my Zelda games, even though I own more of those. And the reasonfor that should be pretty easy to figure out :p Pokemon has an insanely high replay value as well as lots of post-game content for most of the games, with how every playthrough of any game can be different by mixing up your teams doing challenges, as well as catching legendaries, EV training for competitive battling, etc. for the post-game, and so on, which is far from anything that can really be found in any of the Zelda games. The fun in those games mostly lie in the main story, and while progressing through the game, and once you've finished the game, there's just not a whole lot left to do. I mean, of course you could do side-quests, gather all the heart pieces, bottles, etc., but it just doesn't really compare to what Pokemon gives us, and whereas I could easily start over with Pokemon instantly after beating it, and most of the time still enjoy it again because of how every playthrough can differ from the last, I usually can't play a Zelda game twice in a row without getting bored rather quickly during the second playthrough.
So yeah, kinda self-explanatory. I can't really think of any other games that I've really played that much, since those two franchises have been what most of my gaming life has been spent on, and most other games wouldn't nearly get as close :p