The rest of the industry already feels like an afterthought when it comes to coverage. Journalists make sure they cover conferences like Activation, Bethesda, EA, Microsoft, Sony, Square and Ubisoft and the small devs/publishers and indies scarcely get a look-in. Outside the main conferences you have others like CD Projekt Red showing Cyberpunk 2077 behind closed doors. How can smaller companies and indies possibly compete without a massive publisher pushing their wares? There's needs to be more events like PAX and E3 could become that.
Well, first and most obviously, they can be granted a place in one of the platform holder press conferences. The Sony press conference that had the large indy showcase in the middle was good for Sony, good for those specific developers and likely stimulated interest in smaller titles in general. MS has been pretty good since in featuring ID@Xbox titles as part of their presser. Yes, this can be done at the platform holder's independent events as well, but I think those events draw a different audience with more specific interests.
Secondly, E3 causes more people to pay more attention to gaming in general. Someone who may not follow gaming news on a daily or even weekly basis may be more willing to have their eyes on gaming news for a few days in June. As a smaller developer or publisher it may be enough for a larger to audience to be exposed to a small news blurb on a gaming news site to build a greater awareness of your upcoming title.
If each major company has their own events, at various times of the year and those companies become the primary source of coverage of those events, things that happen around and in between those events will get less notice than they would if everything were happening at the same time and coverage is being provided by "independent" sources.