Remember when E3 banned booth babes and turned on the light......E3 has been dead for years but I am glad it finally came crashing down
That's really where the decline set in, honestly
That was just a part of it, although it does relate to the general loss of "eye-candy" throughout E3. I do recall in at least one E3 convention there were also some "booth hunks" too, advertising for one of the games. In their attempt to clean up for a more general audience, a lot of the decor (both static and human) and swag also went away, going from large, detailed statues and displays and the occasional booth babe/hunk/cosplayer to boring cardboard cutouts or visual-only promos on display TVs next to the stands, and going from demo disks, nice quality bags, figures, mugs, and other fancy limited-time swag to mostly boring keychains, card holders, lanyards, and cheap OEM junk with a brand label slapped on (such as a cheap reusable cup just with a gaming company's name slapped on).
Basically, they went from embracing some of the nerdiness to trying to appease everyone, and it ended up not being worth its value even in the years prior to COVID.
Ironically, the best place to find some informal game booths are at anime conventions. I recall seeing a Square Enix booth at one, with two hired cosplayers dressed up as Tifa and Cloud. There's that odd overlap where games are now being associated with anime to some degree, given that you can also find God of War and Halo cosplayers at an anime convention. I wouldn't be surprised if more gaming companies shift over to some degree.