I dont know, but i find it quite convenient to craft that ropes and cords.
I mean, it could make things a lot more complicated, because you add an extra option in the action menu, the game handling could suffer, there can be new bugs etc, etc...
Unless sami's got a real smart simple programming answer to that. (Perhaps add a little option, like "half the length of the rope"??)
To try helping out a little:
make that cords and ropes in batches with the "r" command. dropping all what you dont need makes it easier.
Also, to simplify cutting, you can cut for example the 4 ft withes into 2 ft pieces. then when you select cutting thos smaller ones, the game automatically cuts them in half, for example if you want to smoke or dry and not waste tying equip.
Furthermore, if you are using withes from saplings for a trap fence, you dont have to cut them anyway, because the have already the right length.
(thats what sami is saying actually)
One thing the game doesnt do, but should(i think), would be cutting 3 ft automatically as well(as there is also only one option to cut that length. Doesnt matter if you cut 1ft or 2ft from that, the result is the same- 1+2, or 2+1...)