what exactly do you mean by "should be"? as in where do you draw the line of them being skewed acceptably or too much? Also, these blanket statements that so many states never sent a native to Congress don't account for the fact that some of these states (perhaps many) - don't have an Indian population to start with, kind of hard to send a native when there are none.
The Congress is voted in by the people in all states. Only people who chose to run get voted on and usually there are multiple choices. Many people don't vote - that's a problem. Many people vote based on logic similar to picking horses at the races, ie via the name alone - another problem. Many people fit the category, but don't care to run for office. For example - many in the latino communities do NOT speak English... which is a problem in terms of running for office. There are so many factors in place that it's silly to bring up these kinds of stats as some sort of meaningful explanation why the Congress "doesn't represent" America. Even for the ones that are in the office and do neatly fit one of these categories - one could argue that what they do doesn't represent America, but it's not because of the category they're in, but because they do take some inept actions.