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Private utility companies are often subjected to regulatory board controls. Their local monopoly is limited by a representative (supposedly) of the public's interests. That low-risk investment has its potential returns limited to what a board deems "reasonable".

Some states regulate residential housing, or at least taxes on it, to limit what municipalities and counties may do with their taxing authority. It wouldn't be much of a stretch to regulate the rents charged by "housing provider" individuals or companies to be, on average, 1/3 of average local income.