I'm not a believer in the broody instinct has been bred out of some breeds of hen. I sincerely hope nobody can produce any evidence that this so. It is such a basic drive that any hen bred to the point of allowing self extinction isn't really a hen at all.
I do believe some breeds are more inclined to go broody than others.
There are quite a few pieces of anecdotal evidence claiming that a particular breed ascribed to be non broody will in fact sit given the right conditions.
In some keeping arrangements a hen doesn't get many of the stimuli that may help to encourage broody behavior. Imo and it is an opinion but it is based to some extent on observations here, the presence of a rooster may help, as can a healthy pile of eggs and in particular, the sight of another broody hen.