I'd say it's multiple reasons.
- PS4 is the market leader and that isn't going to change regardless of anything.
- Ever game Sony has coming out has been shown at the last 3 E3's (last year was mostly previously shown games)
- ride the waves on cruise control, announce the PS5 E3 2020, Launch 2021
Legit. My reasons why Sony are taking a back seat to E3 next year.
* Scarlett: It will be announced in some form or fashion and there's a very good chance it will be more powerful than the PS5. Doubtful that MS will announce specs, but you can be sure, their going to toss out impressive numbers. Sony won't risk that with their new hardware.
* There will be at least two new Ip's from two of the new studios Microsoft currently acquired. Two are assuredly Ninja Theory and probably Obisdian. Two heavy hitters.
* Halo Infinite will more than likely make some kind of appearance. This includes Gears 5. Both names carry enormous weight still. Especially when you consider both are taking new directions that gamers are talking about. Haters be damned.
* There will probably be at least two to three more acquisitions announced to join the MS family.
*Gamepass will most definitely get a few more 3rd party games to join the ranks in conjunction with more BC titles. And Halo Infinite and Gears 5 will be day one on Gamepass.
* More 3rd party games coming to Xbox.
*XCloud is supposed to make an announcement at this coming E3.
* Sony has games slated for next year for sure. But people have seen or heard about them all ready. PS5 games arent ready to show yet, so those will still be in the oven.
Don't misunderstand - not one of these are said to make Sony take a back seat to E3 in-and-of themselves. But if you have a Microsoft presser containing all of it, that's another scenario altogether and could hurt Sony's enormous momentum moving onward to next gen.
Like I stated before, Sony won't have the benefit of Microsoft stumbling over its message or talking about TV, TV, TV or DRM -- none of that. Like it or not, Microsoft is poised to make a HUGE splash at this coming E3. In my humble opinion, Sony doesnt want to approach the show with only games we know about, and PS5 games wont be ready to present yet. And I dont think PS5 is quite ready to be shown just yet.
With everything I've just mentioned, I think Sony is willing to forfeit E3 2019 and would rather show what they have during another event they have much more control over, and dont have to share the lime light. Just in case the competition is full on ready. And frankly, it looks like they are.