In my area (250k people, Iowa) there are 2 health groups.
I actively tried finding a PCP who wasn't part of the two health groups but accepted insurance - as mega health groups greatly increase the total cost of care. I gave up after looking up about 20 from the hundred or so names insurance sent me. Basically everyone
Unity Point recently announced it wouldn't be merging with Sanford health group. That would have expanded Sanford's strong footing in northwest Iowa, gaining 5 hospitals in Des Moines and at least one hospital in most locally large cities across the east half of state.
It's hard enough to make the math work for hospitals in rural areas. The merger would have made it more difficult for the entire region to find competition.