Developers can make different types of games that are not thematically the same as their previous ones, and they dont need it all smashed together into a word because its just a different game
There's no "souls" in sekiro basically so there's no need to shoehorn it into the "genre"
- Souls-like is the genre.
- Soulsborne is the series that includes Demon's Souls, Bloodborne, and the three Dark Souls games.
Sekiro may or may not be covered by the former already, but is too different to be part of the latter, so there's zero need to add its name to either term.