The playing field is different. The reason commercial broadcasters are so protective are regulations itself. Commercial frequencies are auctioned to the highest bidder. In non-commercial radio you apply and fight off competitors until you are the last applicant standing.
A commercial frequency can easily run you six figures to win the auction, then you start at square one, just like the non-commercial FM. You might shell out hundreds of thousands of dollars then half a million more buying land and building a facility that is a commercial FM. The non-commercial FM pays to build plus any actual expenses of any candidate that applied against you. The result is a commercial station might cost double the investment of a non-commercial station.
The up front dollars make commercial radio operators very protective of their position because they need every dime they can get. The non-commercial FM needs every dime they can get too but up front dollars are less.
Stations that are commercial pay an annual fee to the FCC based on the market. It is sort of like the FCC is charging property taxes. Speaking of that, non-profits are typically 501c3 organizations so, that gives them an added advantage on taxes.
With that said, I can tell you lots of radio stations on the commercial and non-commercial side, especially away from the biggest markets, are not very good at getting across the value of the commercial or underwriting. Trust me, that you play ten in a row every hour or have more winners than your competitor leaves the business owner scratching their heads and asking how that makes them money. Sure that is important but not to the business owner. Public radio touting the Halo Effect, that people will love you because you support their station, is a nice feature, but really pretty lame compared to the concerns of increasing customer count, increasing ticket price, etc. The Halo Effect is like adding sprinkles to your ice cream sundae. Granted, you want sprinkles but let's talk about the ice cream and toppings.
To many commercial stations walk out packages and reps with zero training to handle the marketing for businesses. You must know the business, their goals and how they currently do things. If you do that and only sell what you believe will produce the results they want and help them toward their goals, you'll make a trusted business friend they value too much to cancel. If your media kit is not written for the business owner, you lose.
Another thing non-commercial radio does is educate the client on Underwriting Rules. There are ways to resolve this without making the sale difficult. We barely understand Underwriting and the average business owner thinks it is something the insurance company does. That's like needing a timing belt on your car and the mechanic insists on showing and explaining how the belt is replaced. Telling a client what they can and cannot say is a great way to convince them to spend their marketing dollars elsewhere. You say this is what we do and how we phrase things because our listeners respond to this. Anything else you want said goes on our website.
And don't get me started on calling it a donation. A donation means you hand over money for someone else's benefit. Marketing dollars are an investment that provides a return to the investor, the client.