Even if this were true (and I’m skeptical that it is), don’t forget that, compared to 2017, a lot more people are at home watching TV in the middle of the day due to, you know, pandemic, layoffs, quarantines, work-from-home, distance-learning, yada yada yada.
Conservatives largely don’t watch the legacy media anymore. Most of us watch things online now. The propagandists simply didn’t bother counting the majority of Trump’s actual supporters and how they viewed his speech.