There are probably several ways to analyze it. One way:

The demographics of "late night TV" probably skew "young and poor" on average (older people go to bed earlier and have cable or streaming services and don't rely on broadcast TV). This is probably somewhat different than previous decades when there were only 3 stations. Moreover, the biggest cohort of the population is Boomers who were up later back in the 60s-80s and now go to bed earlier

Then there is Marshall Mcluhan's theory on how TV content should relate to Ads to maximize their effect. In essence, his theory was that TV content should skew negative and provoke tension in the viewer. In sharp contrast, Ads should be overwhelming positive (to the point of simplicity). This combination provides the viewer "emotional relief" during the Ads - and thus a receptive state of mind to better absorb the advertising message.