Sure but they're a decent option for places that don't have the ability to build underground (Florida for example). I wonder how they compare to the New York subway's over road rails.
The Simpsons did an episode where a monorail salesman tries to sell Springfield on installing a monorail, and there’s a song somewhat evoking the 76 Trombones scene from the musical The Music Man by Meredith Wilson. Mine and other comments are lyrics from that song.
New York has older bridge designs made of loud steel. Concrete is much quieter and what modern elevated rail systems use.
Monorail might be slightly better for all elevated rail, but it is much worse underground and cannot run on the ground at all. Since both of those are useful at times you should buuld a regular two track train. Plus monorail is not standard so if you build one it will come down in 20-30 years when you can't fix something anymore. Meanwhile regular trains have been running more than 100 years.