He was ignored because it was irrelevant to the impeachment investigations.
You're acting as if Hunter's appointment to the Burisma board was some kind of secret. It wasn't. In fact it was openly discussed in the media at the time and the concerns that Kent brought up in his testimony were debated in the press. See for example
this article from December 2015 by NYT. In fact, this article raises the exact point:
Hilariously, this quandry serves to demolish the Republican claim that Joe Biden was attempting to protect his son; indeed, he was doing the opposite, as laid out in contemporary news sources such as this one.
This is an unsubstantiated claim by a Federalist article so it's not worth addressing.
I don't know why Republicans of all people fail to understand how capitalism works. Hunter doesn't need any experience in natural gas to be on the Board of Directors of Burisma. Have you looked at a single corporate board in your life? Disney has the head of a biotech company. Can you tell me what that has to do with what Disney does? They also have an executive of an auto company. You could level the same charge against them. And yet you don't, because Board Directors very regularly don't have exact experience in the industry on whose board they sit.
And $50,000 a month is a fairly standard Board salary so attempting to claim that that's some kind of illicit payment just makes the Federalist look like a bunch of morons.
Finally, it doesn't matter if Hunter's name helped secure the role. In fact, again, that's how capitalism works. Board Directors aren't hired for their industry expertise. They're hired for their business connections and high level business experience. In Hunter's case, it's obvious that he has plenty of connections that would be useful; additionally, he has ample experience in cross-border legal work. It makes perfect sense why he'd be a Board Director.
Indeed, it's quite the opposite, as the article from 2015 above blatantly shows. Your article and conspiracy theory are a complete joke.