We used to sell sausage to a mainstream bakers, and it is radically different to regular sausagemeat.
Mainly consists of fat and rusk,and something called nupro, which binds water to protein.
Eg.
The meat content of sausagemeat in a retail butchers is 70% but usually a lot more, but in bakers sausage its about 15%, which is why it tastes so pasty.
Personally having made it I NEVER eat sausage products like sausage rolls out of bakers. Yuck a doo 😡
Incidentally you cant make sausage from very high meat content or it becomes dry and tough. Worked for a chap who used lean instead of brock(trimmings) and we in the shop all felt there was not enough fat to keep the product moist.
He made nice pork sausages though. Basically took an entire gigot of pork , skinned it, chopped it up, trimmed out any gristle and minced the entire thing as the basis.