MediaWorks management viewed Campbell Live's crusading journalism as a liability that stretched audience patience, company sources say.
The show's ongoing coverage of Pike River, where 29 men died in a 2010 explosion at a West Coast coal mine, was specifically singled out by management as having led to viewer "fatigue".
The term "fatigue" struck a sour note last night with Bernie Monk, spokesman for families of the dead mine workers.
"I can't believe that would be one of the aspects of getting rid of John," he said.
"Sure Campbell Live covered a lot of it but TV One did a hell of a lot too and they are still willing to do that.
"Campbell Live was a great ally in getting the truth out and I felt he was never over the top or on a crusade by any means."
The review by management - which concluded on Thursday with host John Campbell leaving the network and the show facing replacement within the next six weeks - also considered Campbell Live over-emphasised charitable fundraising and coverage of the aftermath of the Christchurch earthquake, GCSB spying and child poverty.
Campbell was said to be leaving the channel "to take a break", after the long-serving host declined an offer to remain with the channel, albeit with a co-host and not necessarily long-term with the presently constituted Campbell Live.
A replacement show, with two yet-to-be-cast co-hosts, is understood to be shaped by these criticisms and will have more of an entertainment focus and more oversight by MediaWorks executives.
Rachel Smalley, presenter of Newstalk ZB's weekday Early Edition programme, is among those being mentioned as contenders to front the new TV3 show.
Sources inside MediaWorks said the decision to air replacement current affairs only four week nights, with the Friday broadcast axed in favour of entertainment programming, would see the show's current staff cut from 22 to 16.
Interviews with current staff to fill the reduced job pool expected to take place next week.
The replacement show, hoped to air its debut episode in early July, is also subject to a formal review of its own before the end of the year.
This week's decision followed a six-week-long review period that generated significant levels of public interest and activism, with tens of thousands of people signing petitions to save the show and public meetings to discuss the future of journalism.
A ratings boost that accompanied publicity around the review, and had seen Campbell Live regularly become TV3's most-watched show, was ruled by management to be "unsustainable" without major changes, the source said.
A MediaWorks spokeswoman said it was not appropriate to comment on the employment process. But the replacement show would have a broader mix of stories, and be more relevant to the network's audience.
"The story mix will include the content TV3 is known for, including following important stories and issues, and high quality journalism.
She rejected "conspiracy theories" about the timing of the Campbell Live announcement, which came minutes before the Government unveiled its 2015 Budget.
"The announcement was originally planned for lunchtime Wednesday, and delayed twice to give John more time to consider his position. It was eventually made at 1.40pm Thursday."