Why would a vendor pay someone else for an online-only expo when they can market directly via ads? Why would a customer pay to participate in an online-only expo when they can see videos for free online?
Most industries have trade and consumer shows (from film to boardgames to concrete). There's no reason to expect that gaming is somehow unique and should not have one. It's unlikely it will be like the E3 of decades past (or even have the name), but there's value to getting consumers to see/try a bunch of new games.