I wonder if they saw what Nintendo did with the new Zelda series being capped at 2 games and felt the same way. That they’ve exhausted what they could from this world and want to do something new. Elden Ring is my first and only FS game but I wouldn’t mind them doing something new after an apparently extensive DLC.
God of War reboot capped it at 2 games, too. I don't know. FromSoft has gone both ways. They have the Souls series and Armored Core series, but Bloodborne and Sekrio were standalone. So far, they've not given in to the calls for sequels on those. I think Sony owns Bloodborne, so it's not entirely up to them, but Sony would be crazy to not greenlight Bloodborne 2 if that's what FromSoft wanted.
I played Elden Ring after Bloodborne and Sekiro, but since I've played Demon's Souls, Dark Souls 3, and most of Dark Souls 1. I still love all of them, but you begin to see that they reused a lot ideas throughout. Bloodborne reused some stuff, too, but aesthetically and gameplay-wise it's different enough IMO. I didn't know it at the time, but Elden Ring is a very refined, open world Dark Souls 4. Different world and lore and whatnot, but it's still knights&armor, dragons, skeletons, etc. I just know after the DLC, I'll be ready for something entirely new and not just another iteration.