Not my place to say but, letting people trade seeds and cuts could result in some very upset farmers in the end because not everyone is honest about their gear. In this case, the farmer buying seeds or cuts of the forums would act this way on the accounts of trusting this site and the growers on it. Thats just bad.
You can also see that if thats allowed, the farm, which people use to get information about growing, could rapidly decline into a second class site with spams or ads popping up everywhere.
And what to do if some undercover asshole was trying to leak info?
Personally, i like the policy. I can get seeds from many many places including this seedbank but the forum is a seperate platform. Again the rules are made by Logic and this is only my reasoning.