All I know is when I emailed Hornady about no longer listing the .41 FTX, I never got a response. They were a 190 grain Flex Tip for the 41 Rem Mag Marlins. Marlin stopped making the rifle and I guess Hornady decided they didn't need to make the bullet any longer.
I can't imagine a lot of demand for .41 Mag bullets for a carbine. I wonder how many of those rifles actually exist.
Pretty much all companies discontinue items for the same reason - lack of demand.