And when you do 400’ and 1000’ feet is somehow different and 3 times cheaper???
No frame numbers for one - just key codes. And those integrated motion picture finishing machines are as fast/efficient/automated as the machines that slit, perforate and spool into 35mm cassettes.
The 100 foot loads are in a legacy format that the modern equipment cannot be made to produce. And their volume is so miniscule that it would never be economic to invest in machines for the 100 foot loads that would, through speed and automation, materially lower costs.
It is similar, in many ways, as the situation for 220 film, except that the 100 foot load machine is still working.
One of the other factors that affects this is that the slitting and perforating parts of the process are a leftover from the days when they were mainly used for high volumes of motion picture projection print stock. Those volumes contributed some economies of scale, the benefits of which were shared in part by the 100 foot loads sold in relatively high quantities into the school photo and identification photo markets, where cameras with 100 foot load magazines were often employed.
Historically, 100 foot loads were never directed to individual hobby users or students trying to save money. The small amount of product that made it into the retail environment serving those types of users was just a fortunate byproduct of the commercial high volume users' needs. None of that high volume use remains. And of the relatively small number of users who currently buy 100 foot loads, only a small percentage would be willing to deal with 400 foot or 1000 foot loads instead.
.