Many patients are uninsured, underinsured, or have access restricted by insurance plan terms.
Many patients could afford reasonably priced health care but not the inflated prices charged to individuals, which are often much higher than the payments accepted by providers from contracted insurance companies (discounted prices).
Most providers have to spend much less effort on collecting payment from contracted insurance companies than from individual patients, with some patients not paying at all.
Most providers would like to provide medical services to more patients if they feel confident they will get paid.
Telephone time of healthcare providers is usually not reimbursed; services that require healthcare provider judgement, documentation, and entail legal liability can sometimes be provided on the telephone but providers may require office visits so that the services can be paid for.
Insurance companies are taking 10-20% of all healthcare transactions.
A single payer guaranteed healthcare system will very likely have initial overuse, followed by rationing, or increasingly complex authorization system for services, taking away resources from treating patients.