Possibly because you don't understand gardenbanter? It's not a gardening forum, it's in effect a messaging service which posts your posts to a newsgroup called uk.rec.gardening, and collects and displays posts other people make to the newsgroup.

The newsgroup isn't a question and answer service, it's a group for chat about gardening, so while people will try to answer your question, they will also take the conversation off into quite independent routes. So asking people to stick to your subject comes across as a wee bit rude in that context.