For profit hospitals and doctors do not have to accept medicare or medicaid patients. Non-profits are required to to get non-profit tax exempt status. Some providers are more efficient then others so a statement that medicare reimburses below cost is not accurate. Maybe some procedures reimburse below cost but not all do. It is also not rational for these profit seeking doctors/hospitals to accept medicare patients but they do which directly conflicts with your statement that hospitals only do profitable things. One could argue that medicaid and medicare patients are sicker and there are more of them than most so they provide a larger revenue stream than private insurance covered patients (and they also require more procedures). If you didn't have these patients then your utilization would be lower and therefore your COGs would be higher as well. Also you might not be able to scale your hospital to take on the profitable procedures. Residents are also lower paid which give the hospital greater incentive to have them treat the medicaid/medicare patients as well. So logically it is better to employ more residents if you have sufficient patient load since it would reduce COGs.