In theory, you could ban all "political advertisements". In reality, you need an enforcement mechanism, which comes with regulators, prosecutors, etc... You also get a government board or committee to setup rules defining what is allowed and what isn't under your law banning "political advertisements".
Pretty soon, that board is run by either big media companies or else entrenched political consultants, because hey, they're the ones that really care enough to really study the laws and the regulations and gosh darn it, they have all sorts of relevant experience that makes them perfect for the job, right? So the board starts defining terms like "political" and "advertisement". Is a movie about events in Benghazi political? Is it an advertisement? Perhaps that depends on who is making the movie, some right-wing group, of course it's political. Hollywood? Of course not, they're not political, right? Maybe it depends on if Hilary or Obama are mentioned by name in the movie or not? Or perhaps we can just exclude stuff like that when it's shown say, within 60 days of an election where people mentioned in the move are involved?
Not sure if you're movie is going to fall afoul of the regulations? Better to just make sure your movie gets pre-clearance from the regulators who report to the board. That way you can be sure you aren't wasting your money on that Benghazi movie the government will order you to not release, or fine you or throw you in prison for showing.
Of course, like with all other laws, there's prosecutorial discretion. I mean, we have to allow for the prosecutor to have some common sense in only going after the actual bad guys, right? Maybe if the prosecuting attorney happens to be appointed by someone who is politically friendly to you, you get a little more leeway in what kind of movies and advertisements you can put out there? Perhaps everyone knows that if old Joe wasn't the prosecutor, you couldn't put that union "Let's all work together!" ad out there because someone else might call it political, but since Joe doesn't prosecute that sort of thing, you're ok.
I mean, it's not as if your elected and bureaucratic representatives have any incentives around caring which politicians get elected, right? No incentive to ensure the system can be gamed for their benefit?
Hopefully you can begin to see why banning "political advertisements" is in effect, the same as giving whoever is in power a filter to tilt media and advertising in their direction. That's what campaign finance "reform" has always been about in Congress in this country. Gaining an advantage over your political foes, tilting the playing field and ensuring you keep power.
Fortunately, we (all forms) have a right to free speech and the current supreme court is interested in preserving it more than they're interested in letting those in power in the government restrict it.