IIRC the first "modern" monorail. was proposed in the 1830's.... Seattle is famous for very limited ride they built for the World's Fair, back in 1960, to show us all this "modern" future, we'd by sharing with the Jetson's. Disneyland built one in Anaheim, once did propose one from LA to Anaheim, and later built a much higher capacity monorail for Epcot/Orlando Disney World. And, there are a handful of monorails, here and there, around the world, most often used as "stand alone" fixed guideway "circulators", or for things like airport "connectors". There are some real good examples of this in Japan.

I've been around for several of the "perennial" monorail proposals for LA, or the Valley. One guy was famous as the "monorail" guy, who married an heiress, and would come to agency meetings back in the 90's, and propose things like building a monorail down the middle of the Ventura Freeway in the Valley...

This build it down the middle of the freeway, it would be so "easy" it one line you hear from those who seem to believe this "technology" is somehow magical in being somehow cheaper or easier to construct. These proposals for the Valley, come back like zombies, despite the fact that the 101 was built to intentionally "avoid" taking expensive commercial land takes, by threading through relatively low density (back then more than today) back in the 1950's, when they built it. And, despite the that such a 101 monorail line would not actually serve the mostly some distance "off-freeway" employment, entertainment, commercial, or educational institutions, that generate actual transit trips, by providing direct access. And thus, was inevitably a very poor performing "fixed guideway" transit option for that corridor in terms of ridership (at least Pasadena has high population and employment density adjacent to most of the current I-210 LRT stations...).

There is nothing special about Monorails, (or People Movers, or Maglev for that matter), these are another mode of a "fixed guideway" rail transit system, as are LRT, or a Subway system, in terms of travel time, or access issues. Nor is there any real evidence of any significant construction or operational cost advantage from any of these proposed transit system applications, having only one rail, instead of two.

Monorails require a fully grade separated right of way, usually on an elevated structure, with elevated stations, that really offer no operational benefits, or construction cost differences, from similar elevated bi-rail systems. Although, with a much more limited vendor pool providing equipment. Switches are very costly, and the elevated system, with current "track" designs (center "bar" rail, usually concrete) also makes things like "train" maintenance and storage facilities very costly. Which is probably why you see almost no high volume, multi-stop monorail transit "systems" anywhere.