Sure it's illegal for people to be using non marine radios for hunting or what not, but when you get down to FRS is a waste of time in hunting terrain. So, they got nowhere to go! Okay, so what are you going to do, hire more FCC cops? My guess is they could drag people in right and left and the judge would listen to the offenders BS on how they didn't know and then the judge would say ignorance is not excuse you bought the radio you should learn about then fine them 200 bucks.
In the end you would burn up a lot of money chasing offenders around with no return to pay for it. It's the same thing with poaching, there are now so few game wardens because of budget cuts poachers are decimating sturgeon, deer herds, elk , bear and you name it.
In the end it all comes down to priorities When I see someone on a marine radio I always tell them to stand in a river or lake while they talk!