Today, with the ubiquity of Youtube, Twitch, and other ways of seeing game footage and content, E3 just became another marketing event. And it was an expensive one at that. Publishers and platform holders chafed at the fact that they would have to do a live stage show where gaffes and demo disasters could occur, and marketing departments hated the fact that all of their effort could be easily overshadowed by another company's big reveal. You saw Sony tap out even before the pandemic hit, opting for its own separate showcases where they could control the message and dominate the news cycle. That became the model that more and more companies decided to pursue.
I will miss it because it was a fun event in the middle of May (and later June) that gave you a nice preview of what cool stuff was coming later in the year. There are also some legendary moments from the live presentations over the year, ranging from Sony getting on stage and only stating the price of the Playstation (which could undercut Sega's Saturn by $100, after Sega had decided to rush it for a surprise launch that day) to J Allard introducing the world to the new paradigm of centralized online gaming in 2005.
It's like with cooking steak: you could say well-done is the antonym of rare, I'd agree[†] with that as a premise. But medium doesn't have an antonym, and it makes less sense to describe the antonym of medium-rare as medium-well, they aren't opposites.
[†] If you would prefer "blue" or even "raw" for maximum contrast, that's fine by me, both cool and cold are antonyms[‡] of warm, same principle.
[‡]: https://www.merriam-webster.com/thesaurus/warm