Yup, I remember reading the manual on the toilet while my sibling was playing so when it was my turn, I'd have a leg up. We would take turns, cheering each other on as we got past a difficult part, and sharing secrets that we found.

With the internet, I can just look up a walkthrough pretty soon after the game launches, so I have no reason to look at the manual (if there is one) or talk to anyone else.

I think that's why competitive MP has taken off. People want that social experience, and that's filling in for what used to exist. I remember PvP being a thing, but I also remember helping each other out on a SP game being a thing, so both were social activities (if it wasn't a sibling, it was a friend or coworker).