Well because they xancelled PSX and E3. These a big events where they could announce release dates for their upcoming games and get lots of press. Unless we get a release date at TGS i think it's fair to assume no major Sony game is coming out first half 2019(besides Days Gone) and Sonys second half is usually not full of exclusives since they let third parties get the spotlight. The PS5 is gonna come out in 2020 and it would make sense ot have these major games be cross gen.
Your points are valid. Indeed, title like TLoU and Tsushima use events and lots of press when announcing realease dates and making these moves in a event alongside ps5 makes sense, especialy if sony is planning to promote crossgen games and backward compatibility.
Prediction: In 5 years Nintendo will Lauch a "Core Mario game" very similar to Astro Bot. That said, many will Ignore Astro Bot existence and say Nintendo created this concept.