I don't know why you'd think that the parks would be busy on Valentine's Day. On holidays like Christmas, Easter, and 4th of July it makes sense that the parks would be busy because those are holidays that people have off from school and work, so those are very popular times to visit WDW. In fact, I just checked the February crowd calendar on easywdw.com, and Valentine's Day is given an estimated crowd level of 3, on a scale of 1 being the lowest and 10 being the highest, so crowds are expected to be light that day.