Reasons that come to my mind for a ban: So that HN readers will not be inconvenienced or frustrated by a link they cannot follow. To prevent people making posts

Reasons that come to my mind for a ban: So that HN readers will not be inconvenienced or frustrated by a link they cannot follow. To prevent people making posts for the purpose of driving traffic to their own pay wall website. A reason for allowing them might be that sometimes good stuff is behind a pay wall.