Is PBS not a non-profit? Because they'll give me perks for donating certain levels but won't give them to me if I don't donate at certain levels. There are ple

Is PBS not a non-profit? Because they'll give me perks for donating certain levels but won't give them to me if I don't donate at certain levels. There are plenty of non-profits that give similar benefits if you donate. Even a local garden near me that is a non-profit won't let me enter unless I give a donation. I just don't see the difference here.