Ok seriously what is with anti social dancing agenda of the Sims 4?

I believe it's to leave space for other sims to join without repositioning all the sims every time. Same when they will stand to the side of your sim when having a conversation.

Remember up to 8 sims can join in on group activities, so the angle they pick from/to each other allows 6 more sims to join without having to shuffle around every time another one gets into position.

It's annoying on dates and with smaller groups, but saves a lot of routing fails with bigger ones.