No, I have no idea why these were butchered.
A couple of years ago I was given a heap of A10 parts but it was all like this, everything had been cut, chopped or generally mangled. Most of it was beyond any sort of repair but I did manage to salvage a few bits, these barrels being one of them. I also got a big journal crank that still has one grind left in it.
You have to remember that in the late 60's and 70's this sort of stuff was junk, nobody wanted it and truck loads of good motorcycle parts got taken to the scrap metal dealers. We look at something like these barrels and think "why on earth would you do that" but back then it was junk so to smash a few fins off a set of barrels was of no concern.
That is also the reason I want to salvage these barrels if I can, currently if you need barrels you can search the internet or dealers and find some but in 50 years time who knows so if it is at all possible to save them for future use I would like to.