I believe that this has nothing to do with politics as it pertains to their political positions. It has everything to to with their voices. In case you haven't noticed, both of them when excited and making loud speeches tend to screech. I find screeching very irritating and don't know if I could listen to that for four years. I don't know about you but I don't like being screeched at. Also, I wouldn't want a screecher traveling the world representing the USA.
Yes, I know this is politically incorrect to say what I just said, but I think a lot of people feel the same as I do. So, whether it is said or not, voters will take this into account, at least those who don't like being screeched at.
The truth is, I like them both.... but just don't want to listen to them every night on the news.