I think that it's not 120 is thinner, but that 35mm is thicker to prevent it from tearing out the perforations, you could probably coat it on the same base if the base was polyester so that it wouldn't tear so easily. sheet film base is thicker still to give it stiffness needed so it doesn't slump down in the film holder. A thinner film would require a different focus adjustment just like a thicker one would.
You must be blocking me and others. We explained the reason! It is that 120 is thinner due to the backing paper.
Quelle horreur... Here we go again, picking over the carcass of Kodachrome! Move along. Nothing more to see here.
(elsewhere, a lively thread, again speculating on the Resurrection Day of Kodachrome, is in full swing...)
Why can't people accept the fact that Kodachrome is dead and move on ? why do they still "clutch at straws"?
Because even Michelangelo had a favorite set of chisels?
"When making a portrait, my approach is quite the same as when I am portraying a rock. I do not wish to impose my personality upon the sitter, but, keeping myself open to receive reactions from his own special ego, record this with nothing added: except of course when I am working professionally, when money enters in,—then for a price, I become a liar..."
— Edward Weston, Daybooks, Vol. II, February 2, 1932