Do you think that text-books don't address the misunderstanding? I assure you, they do. When a word is in common usage and there's little impetus to change it then it probably won't change. If many Native American's refer to themselves as Indians and have publications like Indian Country Today why would a word poof out of existence? Because of a mistaken etymology? That makes little sense.

I don't understand why this is asked in /r/askhistorians as its not really a history question.

/u/TibetanPeachPie is correct. This question, while it is related to history, isn't necessarily about history, but more of a social science question.

Yes, the misnomer "Indian" was stuck to Native Americans after Columbus "discovered" the New World, but that isn't the reason why natives are still referred to as such.

But one way to answer is your question is by looking at this from a legal standpoint. In terms of the law, Native Americans are legally titled "Indians" based on past dealings with them.

For example, the various governmental departments responsible for interactions with Native American tribes are termed as such; there is the Bureau of Indian Affairs, Bureau of Indian Education, and so forth. Various laws term tribes as "Indians". You have 'The Federal Indian Trust Responsibility' and the 'Indian Citizenship Act'.

So again, Native Americans are legally cemented with the term "Indian(s)", which aids in reinforcing the title. Is this wrong? That is completely subjective.