Some out of network providers send bills to patients but don't collect. Some even tell the patients not to worry about it, although I believe this may be illegal.
In theory, the high reimbursements are so out of network doctors can get paid market rates. There's also a fair amount of propaganda from insurance companies on this issue which makes the reality hard to discern. Yet they pay 10-20% on average of the bills they receive, so it's just another way to punish the patient while both the insurance company and doctor are taken care of.
For surgery centers, the Affordable Care Act has limited a lot of plans to daily center maxes (on the facility side) so in theory the doctors are being paid market rates for their services. But the differences in prices between Medicare rates and out of network are significant.
In theory, the high reimbursements are so out of network doctors can get paid market rates. There's also a fair amount of propaganda from insurance companies on this issue which makes the reality hard to discern. Yet they pay 10-20% on average of the bills they receive, so it's just another way to punish the patient while both the insurance company and doctor are taken care of.