If it's a poor selling feature, explain that to the guys buying NR length barrels for their ACRs and caliber conversion kits for their XCRs. Yes - while I know that, unlike an ACR or XCR, changing the length will never change an ARs status in this country, some people may prefer the option of different length barrel or caliber for different applications, matches, target shooting, tournament, etc.
Although I agree, that removing/reinstalling a barrel is not the MOST accurate - it will probably be more than accurate enough for most. Having to rezero an opitic after a barrel/caliber change may be a small expense in some ammo and time for some compared to buying a dedicatd upper and optic