The Montana class was designed to go toe-to-toe against the Yamato class. So, speed was sacrificed for guns and armor. But, the battleship had become obsolete. Aircraft carriers and submarines ruled. So, the Navy cancelled the Montana class, and kept producing fast Iowa class battleships, capable of escorting carrier strike fleets, for a while.
The Montanas, like the Midways, were too big to fit through the Panama Canal locks. An additional set of locks, big enough for them, was planned and started. But the steel for the locks, and the Montanas, was redirected to other programs.
Incidentally, those third set of locks were revisited due to the increasing numbers of Post-Panamax ships and are almost finished. Panama (and their ChiCom backers) got a really nice jump on the effort thanks to all the excavation work done in 1943 or so still being there.
Thousands of fewer lives were put at risk sinking the Yamato class battleships by attacking them with carrier based aircraft than if Montana class battleships had gotten within range with their 16 inch guns.