The problem with maglev is it's *expensive* - every mile of rail needs not only a better-than-normal-rail foundation to survive the stresses of high-speed transit (maglev only eliminates the high-frequency vibrations), but also a "track" of either extremely powerful permanent magnets, or an active maglev system. And reliabilty must be *extremely* high, since losing power for even a second means your high-speed train is going to cease to levitate and tear up a goodly length of expensive track, in addition to probably destroying itself and its passengers.
Hyperloop on the other hand is basically just a length of vacuum tubing on stilts, with occasional vacuum pumps along its length to compensate for leakage, and magnetic "mass drivers" wherever there's need for a speed change - all the rest of the cleverness is in the cars themselves, which float on a cushion of air like an air-hockey puck. And anything but the most catastophic of failures will result in the cars coasting to a stop as the air density in the tube gets too high to support their speed. Between the technical simplicity of the tubes, and the long stretches between pylons where the ground doesn't need to be prepared at all, Hyperloop track is potentially cheaper per mile to construct than rail, even in rural areas, and in urban areas rail can't begin to compete.