There's a huge difference between attending an online conference and attending an in-person - you don't have a large number of similarly minded people in a small space for a given time when it's online.
It's been the hardest thing to recreate, the hallway and lunch meetings (basically because it's hard to politely tell everyone to bug off in person but really easy to just log off online).
For most people "watching afterwards" is just another way to say "I'll watch it when I have time".