With the advent of smokeless powder, cleaning rods were removed for a number of reasons, one of which was conversion to a smaller caliber and the old rod was just too large in diameter to fit into the bore.
They were just added weight, and something that got caught on things, usually at the most inconvenient time.
When 19th century rifles went through FTR, cleaning rods were removed, and in many cases, the slot or hole they fit, were plugged/filled.
When the rifles became obsolete, and the cleaning rods were damaged, they weren't worth the effort/expense to replace them.
Many nations started going to separate cleaning kits, with screw together rods.
If you look online, there are likely still some folks making up obsolete cleaning rods for many different firearms.