Okay so it's not the ICC asking the commentators to stop with the negativity, it's Sunset and Vine Asia. From the article it seems like this company is the 'ICC's rights partner' - my guess is they act on behalf of the ICC to manage their TV rights and broadcasting agreements.
This makes a lot of sense to me. Holding is naive to think he can actually say anything he wants on the air. He's being paid to speak on behalf of a company. This isn't him on a free public platform just speaking his mind. He is an employee. There will obviously be restrictions. For sure he's already been told that he can't swear, say hateful things, or spread lies and mis-information while on air. He is already censored to a certain degree, and he accepts that.
On top of that, I think everyone is aware that since this is an ICC event being broadcast all around the world, the people in charge will obviously want it keep squeaky clean. And that means no negative comments directed at any individuals involved, and no fanning the flames of any controversy. They want everything said on air to be cheer-leading the event, the sponsors, the stakeholders, the ICC itself, and cricket as a whole. And that's obvious right? Who could blame them. So it makes sense that they don't want Holding to give casual viewers the impression that this event is poorly run, or that the people involved are incompetent. That just hurts the worldwide perception of Cricket. We've moved on past the 50s and 60s, we don't need fans thinking "Oh yea umpires are biased and ****".
But at the same time - this is not the first time a commentator has talked smack about individuals involved in the game they're commenting on. They talk **** about players and administrators all the time. They highlight umpiring errors all the time. They are unbiased and wear their allegiances on their sleeves. If Sunset and Vine genuinely care about a good, professional, clean broadcast, then why not bring all the other commentators into line too? They should be like how the ICC is with their players, and have a zero-tolerance policy towards any misconduct. Instead, they seem to allow unprofessionalism up to a certain degree, only after which they remind their commentators that they are paid to do a job, and can not just say anything that comes to their minds.
Really though, this is why they should be hiring professional broadcasters to start with, and not just give former cricketers free reign over a microphone during a game.