Because its boring? And ultimately self defeating. Gamers will tire of it in the end. Its why Sony aren't as interesting as they were early this gen. They've lost a lot of their diversity in their portfolio.
??? The bold is contradictory considering their games did not sell as well when they were "interesting," including during the PS2 days. Whether or not gamers will tire of it, Sony has changed their strategy considerably gen to gen, and this is the most successful they've been. There's no argument to be made that it's not a fantastic business decision.
I also don't really see what was interesting about it. Even PS4 owners thought Sony's first party output was lacking at the time. A Killzone sequel, Knack, an Infamous sequel.... Driveclub was interesting considering its social aspects.
The most interesting things were things announced or came out later. Uncharted 4's convoy demo was more interesting than any trailer of those initial PS4 games. Horizon and Dreams' announcements were interesting because they were different, and Horizon was the most exciting thing Horizon announced in ages (and this time wasn't fake like the Killzone 2 video). God of War's trailer was exciting. A high-quality Spidey was exciting. The hordes in Days Gone were exciting. Kojima working with Sony was exciting. And Pixelopus's Concrete Genie was more exciting than Entwined at E3 2014. That's not even getting into how exciting VR is and the kind of experiences you get from it and possibilities like Astro Bot or Blood & Truth or Iron Man.