well yes, I'm sure it is more expensive to print fabric with different widths to suit different sized cuts, though I'm sure when I had a Hobbot, 'Ajax' style shirt, mine had a narrower central stripe than the men's sizes did.
I suspect its because there is 'uneconomic' wastage of cloth that adidas® back out of making shirts with striped sleeves - all the more ironical and sad because the shirts now are made out of 2 dozen? pieces of fabric sewn together whereas, the 1970 England shirt which I am currently modelling is made up of 7 pieces.
In other words, labout costs are cheaper than printing costs, which is very sad. Where are the new kits made?