I don't think there's anything wrong with starting a youtube channel to make an income. That's what it is for most youtubers - once they have enough followers, it's their job.
I follow a number who have grown their channels and make their income this way. They also have sponsors, whose products they flog openly, and "patreons" who choose to support them monthly and who sometimes get extra content. I do think N&M may have overestimated the views they would get, and the ease with which they would grow an audience. I think they probably assumed they would have a few viral videos by now. Their answer to lower numbers than necessary for their lifestyle has been more content and more live content.
To address the pandemic, N&M did more "lives". Lives are, for obvious reasons, the easiest to produce, and I don't blame them for churning them out. Their hook for the pandemic has been the "lives". Some other youtubers I watch have had different strategies.
I follow a lot of youtubers travelling the world in vans who, after broadcasting some exciting videos trying to get themselves and their vehicle homes out of various countries during the beginning of the pandemic, have chosen other new narratives while still living in their vans and RVs but unable to travel - one couple is building a house in the mountains, another is converting a tumbledown stone barn in Portugal into a home, an Italian couple renovated/repaired a simple and inexpensive house and garden in the Italian countryside, another totally rebuilt their tiny-house bus to travel the UK, and another just bought a cabin in the woods in Canada to winterize and live in as they do it. The episodes have a storyline, and there's a lot of drama in stories of couples learning how to build a house as they build a house!
I think the best strategy for N&M would have been to do something as a family during lockdown. Something that would have allowed us to see them grow. All the couples I've mentioned above have grown through the experiences they have documented. They have all been challenged, and they have all grown. So has their viewership.
N&M might have used the lockdown to address the clutter/hoarding issue in a real way. It would have been interesting to see them show us the problem, and then actually get up on the non-LW days and fix it. Day by day, argument by sensible argument, struggle by struggle, but all moving forward, even if with difficulty. There would then be a story arc. There would be a reason to watch. They would actually be overcoming their difficulties in a way that might comfort and inspire others. And they would actually improve their lives and the lives of their children. They could work, via distance technology, with an organizer and coach, who could keep them focused and moving forward.
I'd watch that, and I'd cheer them on.