My digestive system doesn't like to have much if a challenge until I've been vertical for a couple hours, so I tend to be rather hit or miss about breakfast in general, and a 'huge breakfast' for me is a medium-sized bagel with cream cheese and a Diet Coke. I've also got a lifelong aversion to cooked eggs unless they're hidden in something like a meringue pie, so fancy breakfast is utterly wasted on me.

A lot of US States have very tight legal definitions of what can be called a meat sausage or hot dog. Used to have an uncle in Big Food and there were enough states that required only meat + spices and preservatives that it wasn't worth it for them financially to run a different production line that had sausages with cheaper filler ingredients in them and ship them to states with lesser rules.

The American fast food restaurants probably just stick with the strictest state product requirements in the name of consistency from franchise to franchise. It's not necessarily high quality pork, but your McDonald's or Burger King breakfast sandwich is going to be 99% pork by weight.