For everyone that hasn't been playing the game for years already, and are not sure whether they'll actually stick with it for years to come continually to justify the cost of buying the DLC packs.
A 5 bucks entry barrier to what having every pack plays like, is far less of an economic barrier than 14 (soon to be 15) separate DLC gameplay focused packs for a game you don't even know whether you'll like enough to invest that much in.
When paradox introduces a subscription to their content like this, it's not targeted at the forum goers on here that have 5000+ hours in the game already.