Not being in the US, I have to wonder - Why aren't the personnel at a hospital not considered part of 'in-network' while performing their duties at that hospita

Not being in the US, I have to wonder - Why aren't the personnel at a hospital not considered part of 'in-network' while performing their duties at that hospital? If being "in-network" is an important thing, it seems like having "out-of-network" personnel is rather deceitful (I would almost say fraudulent).