Nielsen Business Media, which owns a load of trade publications in addition to PDN, from the fairly well-known (AdWeek) to the true niche (National Jeweler Magazine) has been trying to sell a bunch of its magazines and their related trade shows for months. PDN was on the block, but was not included in the final deal.
PDN exists to sell advertising? They are certainly more altruistic than that.
A more coherent argument is that PDN still exists because of premium subscriptions, for their content, and subsidized by ads.