It not being an RPG probably has a lot to do with this. These creators thrive on replayable games and make most of their revenue from doing specialized runs of these games.
In any given Dark Souls game, you can do at least 5 completely unique runs (Blind First, Level 1, Pyromancer, Miracle Cleric, Sorcerer), plus any number of "X weapon only" runs, plus modded runs like increased aggro and multiplied enemies.
Bloodborne reduced this a lot, since builds were less unique and PS4 exclusivity made the aforementioned modded and "X weapon only" runs impossible. Still, some weapons were different enough to warrant their own exclusive playthroughs.
Sekiro further reduces this. The only unique run options I see are a normal first playthrough, a zero-upgrades run, and some specialized prosthetic upgrade runs (still fundamentally the same playstyle no matter what, though).
It's not that they aren't excited, it's that it just won't be as profitable for them long-term. Nobody can sustain their channel on Sekiro for an entire year.