Much, maybe all, of Mexico supplies single phase power via 2 phases from three phase power. In the US that is known in the power industry as “network power” and is usually 120/208 volts. Now 208 volts sucks. But to get 240 volts from such a configuration, you’d have to have 138.5 volts on line to neutral, and that is a bit too much for most things that want 120 volts. In Mexico they have chosen a compromise where the L-N voltage is just a little high (127 volts) and the L-L voltage is just a little low (220 volts).

electronics-lab.com