It a consumer protection and fair competition thing (and probably anti-fraud too). There are similar rules in place for medicare/medicaid too. Gifts of any kind to induce a patient to choose your facility over any other are forbidden. That's why if you look really closely at ads at pharmacies encouraging Medicare/Medicaid people to switch, even though they talk about all these free things, they're all things that are free if you're on Medicare/Medicaid regardless of what facility you choose. I worked for a place one time that was sued by the feds for giving a $10 grocery store gift card to Medicare/Medicaid recipients if they were the source of a referral. The referral didn't even have to use the company's services, just answer they heard about them from X patient if and when they called for more information. But that was enough to be considered a violation of the laws.
I think the broad theory goes that people receiving these benefits are in pretty tight financial straights and some benefit or discount that might be "nice" to someone else is "essential" to them and may cause them to use your services even when that isn't the best use of their benefits for the purposes of those benefits.