Medicare part A & plan B are the two most common courses of coverage in a Medicare recipients life; It covers nursing and doctor care. It might be a surprise that a Medicare member would need these plans to apply for a Medigap policy, however because medigap supplement plans may not cover additional treatments related to the coverage, Medicare parts A and B are required to insure coverage is covered and patients receive the treatment they may need. Medicare part A & B are required for Medigap eligibility because patient costs need to be controlled.
First and foremost Medicare part A & B is for cost management. If a patient seeking a supplemental treatment needs other treatments to make the treatment effective the patient may end up costing the medical facility more money than necessary to treat. While plan A is given as a default, Medicare needs the premium B to maintain the odds and ends of treatment. If all patients fell on a Medigap plan Medicare would be burdened with the costs when patients need more.
Medicare part A & B must insure that the patient receives adequate care in the facility of admission. Medigap policies are meant to cover what the plans do not. However the same is true of the opposite. As a rule the plans safeguard the patients from being denied the basic essential care they would need while maintaining the costs of the needed to sustain Medicare.
Lastly a Medicare wants their members to get their share of the bills covered by the combination plans. The Medicare membership can be seen as a primary insurance, with the Medigap policy as a secondary. When one does not cover the extent of the coverage, the other follows through, this is the point of Medicare part A & B.