The two big draws are cost and convenience. Many Advantage plans have low or $0 monthly premiums, and most bundle prescription drug coverage (Part D), and often dental, vision, and hearing benefits, into one plan instead of juggling separate policies.
That bundling is genuinely useful for people who want one card, one plan, and predictable extras. But 'low premium' isn't the same as 'low cost overall' — what you pay depends heavily on how much care you actually use during the year.
Slide 3 of 9