||Why can't the city build its own power plant?
It can, in theory. In practicality, however, after incurring the multi-million dollar debt to buy the system - poles, wires, substations, transformer, meters, and more - most cities would lack the borrowing power to build a generating plant. It's unlikely the city would later gain that financial ability because of the ongoing costs of operation, maintenance and capital improvements. That's a big reason that no government utility has formed in Iowa in nearly 30 years. Most existing government utilities built and paid for their own generation years ago or buy cheap federally subsidized power, which is no longer widely available.