This is the likely reason overall, BUT... I still believe some of their plans must have gone differently than planned.
They usually softly transition from one generation to the next, this no-show screams like a huge development blackout, I'd dare comparing to when Nintendo had that owful drought with WiiU early 2013 (for very different reasons though, but still) so that they are completing one last (?) wave of big PS4 projects but aren't ready to show anything PS5-related.
And that's the most worrying thing IMHO, since Sony is also used to hype the hell out of their next big thing, if necessary (Motorstorm anyone?) even with, err, target renders or things like that.
I think in a situation where they don't have much for PS5. They can't do no wrong with making Death Stranding, Ghost of Tsushima and Last of Us 2 Cross Gen. It worked for Zelda. Hell I bet Microsoft will do the same with Halo. And 3rd parties have been doing it forever and same will happen with games like Cyberpunk.
In 2019
- Dreams
- Concrete Genie
- Medievil
- Death Stranding
Then launch PS5 in March 2020 with Ghost of Tsushima as a launch game and a smaller full exclusive from Sony Japan. Then Last of Us 2 as a May/June game. Then by fall they can have a full exclusive again from either Guerilla Games or a contracted 3rd party like inSomniac or Square Enix.