Culture aside, it's an economic issue too. When someone is in a grocery shop and sees beef/chicken/pork/fish at $0.99/lb and sees a bunch of spinach (< 1 lb by weight) for $1+, what are you gonna buy?
Of course, cows are "designed" to do this, while people seemingly are not.
~So yeah, not inherently obesity-preventing.~
The downside is that you will be consuming about 80 grams of oxalic acid. The LD-Lo is 600 mg/kg, meaning that unless you are 135 kg (300 lbs), that much spinach could possibly kill you. Aside from bursting your guts from the inside from the sheer volume of it, that is.
I guess the steaks just kill you more slowly.
While the article mentions meat being more expensive, the rest of the article is filled with quotes like "snacking all day on bits of burger and pizza" and "drink lots of atole – a heavily sweetened corn-based drink". All pretty carb heavy. The article mentions that the dietary changes made are: "eats fast food just once a week, cooks more vegetables, has cut down the number of tortillas".