I used to work a block away from the LA convention center, and went to several E3s pre-Covid--once just bluffing my way in (be 35+, dressed for work, and walk with purpose, and they may not look for a badge) and a few times semi-legitimately thanks to a friend of a friend who worked at Nintendo.
The best part was always just walking around and seeing the spectacle of all the booths, the giant statues of game monsters, the video displays, and the awkward live events. But if you wanted to play a super hot game demo, you were going to stand in line forever. Forget about stuff like the Resident Evil demo where they built a whole house on the show floor, I'm not waiting 3 hours for that. Some let you register for a future slot -- that got me access to play Destiny 2 before release (the Inverted Spire strike), and its Forsaken expansion the next year (Gambit), and as a guardian since Taken King those were very exciting for me. But usually, I walked around for an hour or so and got my fill and left.
When the crowds kept increasing, and the big studios started pulling out at the same time, it already felt less fun to even try to go. I can't imagine what a slog it must have been for the studio employees. I think it would have died soon even if Covid hadn't hastened its demise.