How exactly do they make more money by not paying? They're required to spend 80% of their funds on provider expenses. The only obvious way to sustain the narrative that insurers are distorting the system for profit is the preceding comment's hypo that they'd be over-paying (and then driving rates up as their expenses increased). You propose the opposite fact pattern here.
(Net cost of health insurance, all expenses, is around 6.5% of total US spending, as against 51.5% of direct provider costs for doctors, nurses, and procedures, not counting prescriptions.)
Not to mention, if they can delay payment for a month, that's a month worth of interest on the money in an interest bearing account.