The takedown feature of the Winchester '97 and M12 was not to swap choked barrels but for ease of transport. People were used to the 'leg o' mutton' type of shotgun case for dismantled SxS's and the idea was carried forward with the repeating pump guns. Slightly cheaper models of both were offered with a solid frame.
Remember, there was a time that you could sling your gun case over your shoulder, walk around town, access public transit, etc., without being taken down at gun point, stripped searched and arrested.
Those that wanted to change chokes on solid or takedown models had the option of a fugly 'Polychoke' or 'Cutts Compensator' abominations that totally ruined the looks of a classic design.