Because you are paying in buckets of cash every month.(premiums) in addition to co-pays and/or deductables.
They make money by weasling out of honoring your claims!
(Even if they pay off all claims and then some they still make a barrel of money on float because they take your premiums and invest them in high return securities!)
So if they balk at delivering you a $50 mask part when you need it, then smack them with a 2X4 (but make it look like an accident since I would never reccomend any real violence. Nope. )