Monorails are rubbish. With one exception, the rails are always mahoosive beams that cost vastly more than a traditional track bed. Pointwork requires enormous constructions.
Basically, the whole lot offers very few benefits over a normal railway, while the downsides are terrific.
This doesn't make them any less fascinating of course. Which is why I share with you this film by the Ouse Washes Landscape Partnership covering the TSR2 of the rails - the Hovertrain.