Why is it the Independent presidential candidates don't debate or get to debate?

This is one answer that I found but I believe that Independents should be on the debates. Maybe we would get some facts about what can be done for America and it's people and not a bunch of finger pointing and arguments. This should be changed but I have a feeling that the Dems and GOP have a fix in on this !

To qualify for the stage, a candidate needs to be polling at 15 percent or higher in an average of five major national polls and qualify for the ballot in enough states to have a mathematical chance to win the presidency.

The debates are controlled by the Democratic and Republican parties. The 15% rule is a myth. Ross Perot was polling (7%) less then what Gary Johnson is (9%) before he was asked to debate. After the debate he polled at 19%. It is a skewed system to keep the Democrats and Republicans in control. Here is a link to explain how The Commission on Presidential Debates (CPD) came to be and how they control what the public gets to see. I think they are afraid if they let someone like Johnson, who has no scandals to speak of, to get on stage with Trump and Hillary who are walking scandals.

people.howstuffworks.com/debate4.htm

The 15% requirement is stupid. If they were allowed in the debates, they'd probably be polling higher as a result because it would grant them some visibility. And it might actually force the other candidates to talk about real issues and not these stupid personal drama distractions that only serve to further make American politics a farce.