I'm actually impressed. Those are people that care about their job.
They ran psychological experiments on the children that spanned weeks or months. They deliberately incited them to see what would happen - without any direct guidance or approval from the parents. If I had found out my kids had been subject to these experiments, I would be livid
There are costs to this. Sometimes the kids will fight or some kids will be left out and perhaps adults will need to intervene to get things back to a good baseline. But the benefits are that you become prepared to work, play, and live with other people - knowing that you won't always get your way, and it won't always be fair, but there are ways to handle it.
In the story laid out by the article some kids are monopolizing the legos to the extent that other kids stop playing with the legos. Okay, so? That's good. They found a good solution - other people are using the legos, I will play with something else. Next month when the lego hogs move on to playing with other things, the kids who were playing with other things can go take the legos. Or maybe they won't, but that's okay too because not every niche is for every person all the time.
The resolution is that the teachers lay down rules about how the kids can play with legos. They have to build their buildings to a standard size. The takeaway is that authority will tell you when you can play with your toys and how you can play with them and if you don't abide by the rules you don't get to play. Why is this a better lesson than letting kids play by themselves as much as possible?
It looks like you didn't actually read to the end of the article, given that the resolution is that the teachers get the children to work out their own rules about the Legos that all of them feel is fair.
This is literally the point of the article.
They're showing their clients what a good job they're doing at instilling values and teaching life lessons.
edit: i mistakenly said they're a private business, they're a non-profit.