Reaching as many votes as possible forces parties to draw their discourses around the lowest common denominator, which dumbs it down a lot.
The competition is fierce, so small by small step parties push the boundaries. There's an inverse correlation between the results in the last election with the incentive to push the boundaries. So if you're losing by a wide gap, dumb it down and appeal to emotions even more. Then your competition is forced to react, hopefully not quick enough.
I've been a consultant in a company for political parties for a brief period of time in my country, and the level of technification and specialization is on par, if not better, with the best marketing campaigns in the private sector. I laughed when I saw the scandal about cambridge Analytica. IDK in the US but in Spain microtargeting and segmented audiences were already being used by that time.
It didn't feel right to me so I left before I made a year in it. It wasn't only my job, it was the people I had to speak with, the feeling after the meetings that we were in the hands of completely idiot sociopaths.