The main purpose and intent of the Affordable Care Act was to make it possible for those with pre-existing conditions to obtain health insurance. That has been accomplished but there is a trade-off.
Hospitals and doctors were leaving networks prior to the law but the law has increased those numbers considerably. In order to keep premiums affordable new contracts with healthcare providers had to be created. Many doctors have found those new contract rates unacceptable. Insurers are warning consumers if they want low rates their choices will be limited.
Read more about narrow networks here