This does seem like a superior way to build elevated rail. Less noise in particular, as turning doesn't induce slippage like on a normal train. Wonder why it's so rare.
Most rails lines continue far enough to leave dense urban areas where this makes sense so they have to transition between elevated and ground level tracks which this can't do.
Expensive and impractical, but could be fun at a theme park.
A fictional example of this is the monorail on the Half-Life games, which transitions between straddle-beam and suspended.