MK11 has 3 different Kombat Kard asset sets:
Character assets, which you gain by complete matches with a specific character.
Story assets, which are obtained by progressing in the story or unlocking them in the Krypt.
And then MKX Kutie assets, which I'm not sure how to get yet.
Basically, the reason why this game has less NPCs in Kombat Kard options is because NRS put less time and effort in them in comparison to MKX. In MKX, they took things from previous games, other NPCs that showed up in the story, and comic pages. This game cut corners with customization so that's why there isn't as many NPCs in Kombat Kards.
With that being said, there are more NPCs shown in Kombat Kard customizations than just Kronika, Sektor, and Cyrax. The MKX Kutie icons show Takeda, Ermac, Tanya, Tremor, Ferra/Torr, Kung Jin, and others. Sorry, but you are wrong.