It's really quite simple.
This is a business. This business generates income from the selling of equipment from its members to other members.
This business has rules in place that prohibit the circumnavigation of the standard way transactions are negotiated and completed. Like when individuals Direct Message one another with the intent of working out a private transaction. This is monitored by the business and steps are taken to block certain information that would make this possible and cut them out of the loop. This is separate from 'love letters' from other members. If you get a nasty DM, report it and the moderators will take the appropriate steps against the perpetrator. These two things are mutually exclusive.