We have 4 Wii controllers because when the kids were younger they could play with friends and the games didn't take a lot of explaining.
Going further back, you needed an opponent, probably because the systems were doing all they could to keep track of the action and couldn't generate an opponent, too.
A couple of times my son has had a friend bring an Xbox and monitor over to play in the same room at the same time. Given that most Xbox's are connected to big (and fragile) TVs, a "LAN party" would be quite a feat.
I don't really know, I am old enough to have experienced this, and LAN parties in the late 90s were indeed fun, but they took a lot of planning, expenses, and parents driving you there. I've been online since I was 15 and when we finally didn't have to pay by the minute everything was a lot better. No more coordinating for a full weekend, etc. That said, I have zero negative memories of splitscreen, except that the person who owned the game/console was always a lot better due to more practice...
Going back to when I was a high schooler, I was closeted and in boarding school, which admittedly had a significant built-in social life (that was of little interest to me), but I was also able to have a long distance close friendship for years thanks to Google Talk. I dare say some of my most important and formative social moments in my high school years were over Google Talk with my small group of friends. Sure we had antics in the dorm at my boarding school etc., but these were minor and fleeting interactions versus the deep and meaningful relationships I had over Google Talk, and anyone I actually cared about at boarding school also interacted with me that way, a good bit.
To each their own, I suppose, but I find this unhealthy. I would encourage my child to be interactive in person, not to hide behind the computer. I say this as a WFH IT employee who games - the desire to be away from people in person, the desire not to interact with others, the disdain for in-person contact, are all symptoms of a problem in my view.
I don't mean it to say I think less of people who are like this, or that they are worthy of derision. I simply think it is bad for the individual and the community.