I don't think there is any conspiracy here. Lawn/Gardens have been popular for hundreds of years, at least, for the wealthy. For example, the Gardens of Versailles in France. [1] The United States has more space to person ratio than Europe too. Suburbia is just people spreading out, wanting more privacy, and being able to indulge in those garden like experiences, on a smaller scale.
So I guess my point is, gardens aren't new, and many US residents have the space and the disposable income.