A couple weeks ago, I had to do a presentation on the topic of Native American stereotypes. Part of that was the prevalence of this type of imagery in sports teams branding.
I think one of the bigger issues here is the constant negative portrayal of Native Americans. The average person today when thinking about a Native American probably still has the mental image of a savage warrior who rides on horses and wears headdresses with warpaint...even though that's a complete misconception.
Media portrayal of this stereotype is a huge factor because of the common misrepresentation. When you see a Native American on your TV, it's most likely going to be of an old war movie or a segment on a history channel. Modern day representation is almost non-existent, and when they are shown, it's usually in a negative light. Imo, the Kings logo here feeds into this with the "war bonnet" as found by @solas and the overall warrior-like feel.
On top of all that, you of course have the culture appropriation. Seeing the amount of racial and cultural figured being used as a mascot for profit is mind-boggling, and seeing how in a way we are using this logo for money, it's something that needs to change.
if you'd like a fantastic website that can explain this stuff better than I can, I recommend this one: https://www.ferris.edu/HTMLS/news/jimcrow/native/homepage.htm
there's a section at the end regarding sports franchises.