(Risk of being hacked) x (severity of being hacked) << (Risk of software not delivered) x (severity of not delivered).
(Risk of being hacked): Small.
(Severity of being hacked): Very negative, but localised most likely to a single machine, set of machines, or hospital.
(Risk of Software not Delivered): Pretty high if we go super-security. We are on a budget. There is competition. Who is paying for it?
(Severity of not delivered): Failure to cure at every hospital for every machine.
So, yes, there is a cost, but the benefit of ignoring security, for some sets of numbers on the above, could conceivably exceed it.