There's sometimes a point in packing bags in an interleaved order where bag/carrier numbers are low and the pitch lengths don't conveniently fit capacities if done in-order. That still requires that you know the necessary pitch lengths in order to work out what to do, but having length information on the ropes does at least give more information for little obvious cost.
There can also be the "Which is the next bag?" situation, assuming caves that require multiple bags, and length markers can help in that.
In any case, even if someone tried to only have ropes of lengths 12.5*2^n metres, ropes can easily end up being cut at some point due to wear, ending up outside the scheme, and given that necessary rope lengths vary hugely, if on a proper vertical trip, it can save a lot of rope if a good spread of lengths is available.
If ropes are going to be marked anyway, (which is useful for someone who caves (or even shares a hut) with other people who have ropes, and for identifying ropes on multiply-rigged pitches, etc) there seems no obvious reason not to stick a length on them.