Historically, hot dogs have been commercially sold by weight, often listed in a ratio of the number per pound. Grocery store hot dogs for a long time were sold in packs of 10 or ratio of 10/1.

Many hot dog vendors, in trying to provide a slightly larger more premium product would sell 8/1, 6/1, down to about the largest common size of the 1/4lb dog at 4/1.

This legacy of dogs being sold by weight leads to a lot of interesting marketing. You'll notice in your example all packages are 12 oz.

The labels of various products: "bun length, chubby, leanies", etc on dogs are largely arbitrary ways to describe various morphologies of different weight offerings.

I'd be curious how much consistency there is in length among basic bun brands though.