I'd call that a product of Nintendo's more conservative nature since then. New characters introduced are way more sporadic and often are one-offs. Many of them are from M&L since every other spinoff has seemingly ceased doing more than 1 new character that isn't derivative (eg Pink Gold Peach). Even the main series, when it adds new characters, they're typically not around long (eg Sprixies, though generic enemies have it easier I guess and it remains to be seen with Odyssey stuff)
Personally the conservative approach Nintendo likes to take is one of my biggest pet peeves with the series. I wish they loosened up and let more games make use of the expanded roster and add to it without fear of creating one-offs.
I think it's hilarious that Tatanga is there but not Daisy just due to how well it illustrates the point I try to make sometimes on how his design is obviously different from Bowser, even with the GB limitations, while if you look at Daisy's black and white sprite with no context it could easily be Peach. Just to put the designs in perspective, but which one did Nintendo favor :P They did differentiate her more later so I'm not trying to rag on her (I'm past that tbh, I was way too harsh on Daisy and her fans just because a minority got on my nerves) but I'm just observing the Game Boy sprites and which looks more distinct from what was in Super Mario Bros.
