Are they sending out the 1s and 2s, thinking the 10s are all scalpers and they might run out?
More likely you can kill 100 single unit orders vs 10 ten unit orders per skid of 100...
Once you get into 3,4,5,6,7,8,9 or 10 unit orders you have to spend more time selecting the proper shipping box, packing and sorting... Especially if it's a mixed lot of orders...
Since they use what is likely an optimized fulfillment company, they likely bring out the single unit shipping boxes and packing materials and knock out all the single unit orders first as it's brainless one PKE in the proper size box, then they switch the fulfillment line to the 2 unit orders boxing and packing again brainless 2 PKEs in each proper sized box, and fill those order and so on and so on... Don't underestimate the complications that arise when people have to actually count and decide what box to use in a mixed lot of orders

I had the unfortunate pleasure of working in distribution for a few weeks, and that is the way it was done there, a picker packer put the product on a cart and a skid next to the cart with the proper packaging... You grabbed the cart and skid of and ran with it, brainless as every order was the same so no packing confusion...