TV is the medium of choice for political candidates with money. They believe it is the best way to reach the widest audience. Studies have also shown that negative ads are the best. Why? Because they reinforce and energize the base and (cumulatively) disgust people who are less active in politics. This disgust often causes them to curse all parties and politicians and stay away from the polls. This works to the advantage of parties -- now the votes they get from their partisans count for more.
Negative political ads rely on sound bites and talking points which can be and are repeated ad nauseum. The unpleasantness is initially attractive to TV viewers -- that's a lot of what TV entertainment is about. Crash and burn, shock and violence are the fare even of TV news. It's what we like. Who wants to watch what your representative or president does for his/her constituency every day? We demand that candidates focus on big stuff, spectacular stuff, stuff that's all about me. Negative political ads aim to arouse our emotions, not our thinking powers. And emotions can be aroused very quickly, unlike our thinking powers.
Short negative political ads on TV are especially pernicious.
Requiring such ads to be at least one minute long might help reduce their impact. It's hard to keep up a snarl. Snarfy images get boring very quickly. Sarcasm works best when it drips for only a few seconds. One minute ads will actually require some content and not merely shallow insinuations.
I'm not familiar with advertising prices, but I think maybe a one minute ad might actually be cheaper than two 30 second ones. If political campaigns are worried about viewers getting up to go to the kitchen -- well, they do that anyway. So, politicians of the world: how about it?