Why play something you don't like.
I think he means games we DO like, they just take a long, long time. It's like when your best friend hangs out way too long after a party and everyone else is gone. You're happy to see them, you enjoy their company, but it's late and you're tired and you have to work in the morning. You just keep hoping that any second they'll get the hint and call it a day.
Why do you have to finish it?
Possibly a completionist. Or in some cases maybe we're just hoping for a complete/solid story arc with a beginning, middle and end, even though a lot of games don't do great on that front. But also there is a mindset within the gaming community that affects a lot of us, some more subtly than others, where the logic is that if you didn't FINISH a game, then you haven't fully PLAYED said game. (Obviously this doesn't apply to utterly open-ended games like No Man's Sky or Minecraft, though even those have story arcs you can complete.)
I don't care if I don't see the end. ...(snip) But then I don't want games to end...
I think those are definitely related. I grew up with games that ended, or at least had an "end level". Nothing used to aggravate me quite like games where I reached the end and it just plopped me back to the first level but with harder enemies. There was a degree of satisfaction in "beating" the game, which usually meant seeing the end.
This was a lot easier with, say, adventure games, which were ALL about the story, which were finite. To a lesser extent RPG's, which I think is where the fatigue often sets in for some of us. I still haven't seen the end of the first Divinity: Original Sin, and I have refused to let myself play the sequel until I do, which is foolish because I *paid* for the damn thing, and it's supposed to be better than the first, so I should just suck it up and complete the first one, but I've put SO many hours into it and I've no idea how much further there is until the end.
And sure, I could just go watch a Let's Play on YouTube or something, but as you said, the journey is a significant part of it, so watching someone else do it just isn't the same.
I think sometimes it just feels like the game has filler so it can boast more gameplay hours. The game "Lionheart: Legacy of the Crusader" had a great first act that drew me in, but then it devolved into wave after wave of enemies, and my interest started to plummet significantly. Was there a decent story to be found beyond that seemingly endless gauntlet? Maybe, I'll never know. And it's a shame, because I LOVED the beginning of that game and wanted to love the rest of it as well, but... I just got bored.