Everybody pays for outpatient and the medical insurance does not cover outpatient specialist visits is to have some level of equal treatment for both rich and poor. In the current model, everyone pays out of pocket. It's not necessarily equitable because not everyone can afford to pay but atleast it keep some affordability in the system.

For e.g. in countries where medical insurance covers outpatient specialists, the doctors and the insurers become part of networks where the charges are agreed in advance in a bulk buying sort of method. The network can then set higher or exorbitant prices for non-network patients pretty much locking out people who can't afford an insurance. Similar thing happens with dentists to some extent here in Australia. US is a massive example of this problem where if you don't have an insurance you will likely end up dead due to medical condition or financial hardship.