I guess they thought they made enough on the Raiden Shogun banner?
Even then, why not make some additional money on top of that? Why purposefully make a character that useless? Were they worried that players would be mad if Kokomi had actually been really good, but they used up all their money on the Shogun banner? That also doesn't make sense, because players are still mad that Kokomi isn't all that great.
I honestly don't get some of Mihoyo's gameplay and financial decisions, especially of late. It almost feels like some sort of switch was flipped roughly around the time of the Yoimiya patch.