Maybe they find a buyer in a doctor, maybe they don't, but PE provides them an exit that keeps the practice operating in the community.
Many people don't really run businesses efficiently. There was an interesting video I saw recently where a sole doctor practice made a few changes to their workflow that allowed them to hire more doctors and handle 2x as many people - I would expect a PE firm would pursue similar changes that help increase the number of people they can service, increasing competitiveness and lowering prices in the long run.
I don't know how these tradeoffs interact with patient care, but I wouldn't inherently expect PE to be worse at this than any other operating model.