Don't get me wrong. I am a huge advocate for grade separated mass transit and monorails have a special place in my heart, but at the same time I think that Grade Separated Automated LRT (Light Rapid Transit, not Light Rail Transit) have proven through levels of adoption that they are the better choice. These systems are the rule, not the exception. They are also more flexible because standard or narrow gauge tracks can be built cheaper at grade or underground in areas where the land exists to do so. They can be elevated, at grade or subways all in one.
Their rolling stock is also cheaper and there is no need for more specialized parts or designs meaning lower maintenance costs. A beamway only has the potential to be more economical when in the air because it combines the track, supports and running surface in one which isn't necessary on the ground or underground. This also gets into other more finicky details such as simplified standard railway switching vs. beamway switching. When running a dual right of way, you can more economically put switches in every "x" kilometers to allow trains to switch around sections undergoing maintenance. With monorail beams this is basically impossible. The wider design of their raised platforms also makes LRT systems better during evacuations, excpecially during the need for immediate evacuation. On a monorail, the quickest evacuation is generally a roof hatch and then a ladder down the nose or tail cone onto the beam behind or in front of the train. That or an evacuation chute down onto whatever lies below.