But that’s only part of the story. Market penetration is extremely local. Some entire states, like Alaska, have almost no Medicare Advantage enrollment, and residents there have to choose a Medigap plan to pair with traditional Medicare — or, if they are low-income, a plan for those dually eligible for Medicare and Medicaid.Medicare Advantage plans have become increasingly popular in the last decade and now make up as much as 54% of the marketplace nationwide , according to KFF, a health-policy research gro ...