The purpose of advertising is to prompt action, voting in this case.  The problem is the self-selection bias of the internet and cable news.  My conjecture is that the primary consumers of cable and internet information are the politically partisan.  If that is the case, then the majority of people watching the ad will not change their behavior based on its content.  The money spent on this ad will have failed to capture undecided voters.

Maximum political effect would require the undecided to watch the ad.  The undecided does not know the ad exists, so they cannot be expected to find and watch it on their own.  Television improves visability as the requirement to see the ad is only that one watches TV, not that they are politically active enough to follow cable news or the internet.