The story of the .41 Magnum is a sad mixture of poor decision making and missed opportunities as the result of bad timing, and misreading the market.
During the 50s and 60s, when the revolver was king of the police market, several of the influential gun writers, who had been law enforcement officers, pushed the idea that the ideal police gun would be a 40/41 caliber revolver, pushing a 200ish gr bullet in the 900fps (ish) range. They eventually got that, but it came out too late. What they wanted was a ".41 Special" what they got was a Magnum, which wasn't what they were looking for.
S&W brought out the .41 Mag in 1964. The N frame models 57 and 58 were big heavy guns, but not an automatic deal breaker at the time. What killed the .41 Mag as a possible police round was Remington.
The people running Remington at the time saw the .41 Mag as a hunting round, and focused on producing the 210gr jacketed magnum load, over the lower velocity lead bullet "police" load.
At the time most police agencies tested the .41 Magnum, the only readily available ammo was the magnum load, and that was (properly) deemed unsuitable for police use. By the time the police load was commonly available, most police groups had already made up their minds, and sales to police never amounted to much. Sales on the civilian market have been enough to keep the round and its guns on the production list, but never were enough to put it in the top of the list, as most people wanting magnum power, opt for the .44 over the .41.