Duty Finder does not mean a reduction in difficulty! If anything, it can end up being more challenging due to less experienced or newer players, which is fine - because at least it's a choice, an option that would be available. If the content is being cleared consistently via Duty Finder, and via pugs - then I'd like to imagine it was already relatively easy for Static groups already farming the content long before that.
Friends can help/join/tag along with other friends without being as restricted due to static groups. Without having to resort to stalking chat for groups (which isn't really enjoyable), Newer players and players with erratic schedules would have more access to the content they're paying for too.