I don't think I'm doing either. Just pointing out that the value you get form a pure single player game is very much limited compared to multiplayer.
As an anecdotal example from myself, let's look at Zelda: Ocarina of Time, which I consider to be one of the greatest single player games ever made.
When I first got the game, I played through it in a little under 2 weeks. I was limited to 2h playtime per day (but I sometimes cheated a bit), so I'd say it was around 30h of playtime for the inital run.
Then I did a 2nd playthrough, deathless. Even with having to be more careful, the 2nd run will always be considerable faster, just because you know where everything is and how to solve the puzzles. Took me another week, let's say 15 hours.
A while later, I did the 100% run. But that one was even faster, even if you factor in a couple of hours of routing to prepare. But let's say another 12h.
After that I probably did another playthrough, mixing up clearing order, trying to get my favourite items sooner, etc ... let's say you add another 2 12h runs to be generous. But at that point you kind of have to be deliberately slow to take that long.
But that would give you 81h, at my allowed pace at the time that would take around 2.5 months. Maybe 3-4 if you play less. But after that, the game is finished. It goes on the shelf. Yes, you can get a few more hours out of it every other year, or play self-impossed challanges, pick up speedrunning, etc. But for most people the game will be done.
On the other hand, a game like Smash Brothers or Mario Cart provided me with multiple hundreds of hours of playtime and has potential for even more.