Job security is something a lot of people want but I would have thought the instinct that propels people into acting would also push them into wanting to explore more than one role. Acting seems to be a vocation as opposed to a rational, practical career choice so I just find it unusual when some actors seem to settle into one role at an early age and never move on to new ground.
I'm not talking about soap stars who have left their soap, found that they can't get any other work and so reprise their roles - but the ones who haven't even tested the water and end up getting typecast and almost unusable in other roles.
I do agree with what you're saying, but maybe some get used to the job security? Or maybe if they realise that even if they left, they'd always be associated with that particular role, perhaps they think its just easier to stay?