I believe they are trying to change behavior and get people away from Prime - which they renamed West, which was step one in this process. By changing the name, they're trying to signal that it's not any better than the other two. That's not true, yet, but I think they're working on it. They outgrew Seattle and its convention center years ago, and have said so many times.
Now they're making it a hassle for people to travel to PAX West, figuring people won't want to book flights and hotels unless they're sure they are getting tickets. That favors people who are actually in the geographical region.