IIRC the recoiless rifle was pretty popular around the Korean war.
The problem with the LAW was that it was a one shot weapon. The RPG is relatively cheap , very effective and reusable.
The entire LAW with container takes up less space than the ammunition for the RPG. You don't have to reload the LAW, you just grab another one.
You can reload a recoiless rifle such as the 90mm faster than you can an RPG and it is not much heavier. The laucher for the RPG 7 is not that light.