Mostly because it reinforces/reinforces several stereotypes by associating the group as exotic and savage (less developed).
For example, making their skin literally red. Potentially artistic license, but also very odd considering that isn't a real skin color. Or stating that they were white to begin with and then were turned red, implying a type of deficiency/aberration from "normal" white. Plus the term "redskin" was used historically as a pejorative and associated with contempt, derision, condescension, or sentimental paeans to the noble savage. The stereotype of huge noses also is frowned upon since it was used to make claims of their savagery and brutishness unlike the civilized Europeans. (See also stereotyping Jews as having big noses)
Similarly, the song implies that the entire language is non-sensical words instead of actually being a full language. This is probably the biggest issue. The tribes actually had a full language for communication, not just a bunch of grunts.
It also takes something that would have very specific and special meaning, a war dance, and turns it into a party dance.
The sexism isn't great either. Forcing Wendy to be the aid since she's a girl instead of letting her join in the fun.