My understanding of the Lobbying Act is that the designated public office holder was brought in to capture the communications of these decision-makers with lobbyists. Also, the prohibition faced the issue of the revolving door and whether the individuals could not use any advantages or contacts they had made in performing that particular function as a designated public office holder. The question in terms of debate in Parliament is whether the prohibition should be expanded from what it was introduced for.
On April 20th, 2010. See this statement in context.