Actually Wal-Mart does have health care facilities in some states now[0]. They will probably roll these out as they can but many states have politicians and embedded providers that will fight them tooth and nail. The most common means is through Certificate of Need, this basically means that the claim can be made the hospital or service is not needed as there are sufficient offerings in existence.

They also sell like other stores generic medicines at very low costs; the issue being is some reimbursement setups exclude some of these and some politicians did not like the idea of cheap medicines because it undermined their position.

[0] https://www.walmart.com/cp/care-clinics/1224932