Let's be honest if the government wans someone banned Youtube and the like will comply, wouldn't a government agency want their asset to be seen by as many people as possible ?
Well, if we just entertain the existence of Operation Catboynacht and go by the logic the US government has given in the past, I can think of a few reasons why a fed would selectively limit his visibility:
1. Credibility - given the running theme of Right-wing censorship, getting banned from mainstream platforms I would imagine is seen as a bit of a badge of honor and a mark that you are 'based',
2. Suspension of Reality - YouTube channels that are even slightly non-PC get mass reported easily, and YouTube is notorious for banning first and asking questions later. A 'white nationalist' like Fuentes would get mass reported daily and it would look very suspicious to basically everyone if he lasted longer than a week,
3. Access of Influence - Also, letting him stream on alt-tech sites full of already like-minded people who are looking for him, hear of him through word of mouth or through encrypted back channels is very different from letting him simply air his nonsense for everyone to see - especially when governments and Leftists genuinely believe in the risk of things like alt-Right radicalization and disinformation,
If your goal was to discredit the alt-Right, you wouldn't want to have him compete with videos like this:

Bear in mind, it would be counterproductive to the feds if a "Nazi Ally" was widely seen endorsing Kamala Harris.
4. Risk - Incidents like this demonstrate that the more people know about Nick, the more people are going to try and fuck with him. What Nick did at the door was dumb but in fairness, he's just been doxed and has probably received, like, all of the death threats,
5. Futureproofing - Lots of people suspect Fuentes is a mole after the arrest of the January 6th protestors, so if he were more visible than he is and was exposed as an asset, it would completely vindicate fear of a Deep State. I would imagine any use he has would be to stay networked and relevant while remaining out of the spotlight.
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Personally I think there's a simpler reason for all of this - he got popular saying radical shit he no longer or doesn't believe, got blacklisted for it, was spooked by the feds into co-operating on January 6th and is stuck twisting in the wind to maintain his audience. He expected Harris to win, got it wrong, pivoted to trolling Leftist women on social media with cringe to fit in and was unlucky enough to trend.