Politics is a bit biased, not only because many of these people don't write their own speeches, but also because the complexity of what they say is not neutral. Simpler speech conveys the idea of being no-nonsense and close to the people, while more complexity gives the impression of being intelligent and well thought out.

Depending on who you want to target, you may go one side or the other. For example, republicans tend to use simpler words than democrats to match what their electorate value.