Overall, he isn't entitled to a place in the conversation, but omitting him from certain parts of the conversation seems very disingenuous.
For a real life example, if they show a list of "all" candidates on screen (including 7 that poll lower than Yang), but exclude Yang from that list, this is not cool at all (which is exactly what happened multiple times, as evidenced by the article the parent comment linked). Same goes for debates, where some candidates got a ton of questions asked, while Andrew got way fewer questions.
Consider the economic value to the Trump campaign that comes from how Fox News talks about him. Consider the economic value the Dem candidate will get based on how MSNBC talks about them compared to Trump. It's a huge campaign contributions that aren't accounted for by the FEC but are surely an important part of campaigns.
I do think Sanders was shortchanged of some press coverage in this primary. I think that's changing as his chances of winning go up. I hope he's covered extensively, because I don't think most people are aware of some of his negatives, and as a front funner, his candidacy deserves our scrutiny.
You make a good point that there is an oligopoly of corporate press. I think that's something harmful to our democracy, and something we should be concerned about. I'm not sure what the solution is. For now, I just donate to public radio.
So only the top candidate should get any coverage?!
Ideally, journalists would cover the topics they think are important to their audiences. We know this doesn't play out in practice. But even in an ideal world, I don't see Yang getting more coverage.