The answer is that it's really low maintenance and it prevents erosion while also lowering the complexity of putting in adequate drainage. It's also very efficient to maintain large swaths of grass with uniform equipment, whether it's with push mowers, riding mowers, or tractors.
Maintaining forest is challenging, dangerous, and more labor intensive than you might think. It's real easy to die doing forest work: trees really wanna kill you. Trees are always getting sick and grody. It's easy to accidentally kill healthy trees when you are culling dying/dead trees and, at least for me, making mistakes makes me feel sad and guilty about it. Chainsaws are easy to use and you really have to be not paying attention or not using protective equipment to hurt yourself with them -- it's the trees that are dangerous. This is one of the reasons why suburban developers don't go out of their way to plant forests even if it would make the area look nicer. There's also the question of who would maintain the forest in an area where everything is subdivided into small private plots, but any living forest requires a lot of space to grow.
It is also more intellectually challenging to maintain forest. This is reflected by the difference in wage rates between forestry workers and normal landscapers. Stump removal when you have to do it is also its own set of challenges.
The other reason why uniform lawns are easier to work with is something that only dawned on me after years of letting the weeds grow amidst the normal grass. Weeds grow at different rates and have different impacts on the soil. It's a lot easier to maintain a uniform lawn. A weedy lawn can look cool at some parts of the year with lots of wildflowers and then look crappy at other times when the flowers all die and it's just some weird scratchy bunch of weeds that creates a weird erosion pattern, which is a problem that is more expensive/difficult to fix than just never having it happen in the first place.
I understand the intellectual perspective in this article but the explanation is very silly in light of the practical considerations that become apparent when you are responsible for land yourself. The labor-hour estimate in this article is also totally delusional, or based on some absurd standard that no one actually keeps their tiny lawn to.
I mean, how would you even spent 150 hours a year maintaining a tiny suburban lawn? Are you cutting it with a toenail clipper? Huh? That's almost 3 hours a week, dude.