Often the kids like to play together, but the parents are the ones that are just... weird and asocial. I hate to bring agism into this, but there definitely seems to be a generational gap with the adults.
Some of my kid's friends are raised by their parents, and others are (apparently) raised primarily by grandparents.
When my kid wants to get together with friends whose (50-60 year old) grandparents bring them by, the grandparents come up to the door, socialize for a bit while the kid runs inside, and then we talk about when the playtime will be over and they can come over to pick the kid up. If it's an event where we both bring the kids, I find it easy to shoot the breeze with the grandparents, have small talk about how the week went, and so on.
When the parents are, say, 25-35 year old range, it's a totally different vibe. They'll drive up, let the kid out of the car, and then race away without even getting out of their car. When playtime is at a local park or something, they sometimes hang around, but they go off into a corner, engrossed on their phone, totally ignoring the other parents (who, depending on their own ages are either chit chatting or locked into their Instagram).
I remember when I was a kid in the 80s, and not only would we love to get together at someone's house, but the parents would also be happy to get together for a little socialization, maybe throw some steaks on the grill, put on some Sportsball, or whatever. This practice seems to be dead now that I'm a parent!