The way it works now for selecting Today's featured articles is to choose featured articles representing a variety of topics, with extra weight given to core topics. Meanwhile, we try not to overrepresent some topics (e.g. hurricanes, video games, roads) where we have numerous featured articles. Do you want hurricanes, video games, or roads on the main page nearly all the time?
With the way it works now, if I write a bunch of featured articles on the same topic, then I do so, well aware that they won't all go on the main page. Or if I write a FA about a hurricane, I do so knowing it probably won't be on the main page. Also, some are rather short and perhaps not suitable as TFA. (e.g. http://en.wikipedia.org/wiki/New_York_State_Route_373)
The current situation with one featured article a day may encourage people to write featured articles on underrepresented topics, and core topics, if their articles appearing on the main page is a motivating factor for them.