Campaign ads usually are targetted at voters who don't pay much attention to current events or politics. They say "I hate all that, I ignore the news", which they do for the most part. So, they don't have much real information on which to make a judgment, but many of them feel an obligation to vote. A fancy ad can appeal to them, it's not about issues, it's purely optics. Show the smiling candidate with an enthused crowd and US flag and nice music and say he/she is for "Great things in our future!".
You hope to reach, and influence, 1-3% of the viewers that way.
For Harris right now it's an attempt to persuade Democratic voters she's a great candidate. Her ads will pivot soon.