Because some of us just literally cannot make it there. Like I work 50+ hours a week, at night, and I live in the US. I don't have the time or money/resources to just jump on a plane and all the way across the Atlantic to London to attend a freaking film convention. I wish that I did, but I don't. And I'm not alone in that. And then others just physically cannot get there for whatever reason. And they broadcast a feed online seemingly to compensate for this. Yet the thing that everyone wants to see, tuned into see, it's suddenly "oh you can only see it if you're actually physically here."
That's not fair and it's ridiculous. Especially since a lot of said people probably either live closer to the convention sight, have more money to do this, or more free time on their hands.