Organization matters.
“All of those tasks, in turn, require hundreds of literate, expensive bureaucrats to administer.These are not compatible systems. You can have your bannermen call up their retinues, or you can hire long-service professionals, but you cannot have your bannermen call up an army of long-service professionals”
https://acoup.blog/2019/05/12/new-acquisitions-lannister-infantry-kit-review/