A soccer mom lives based on trends and pop culture, not core, guiding principles. They are highly malleable, sticking their fingers in the air to see which way the wind is blowing. All the while thinking they are deep thinkers. Therefore, their vote is subject to a great deal of what the media leads them to believe.
That is the best explanation I have. Baseball, or football Moms have core beliefs.
A perfect example of a soccer mom is a woman I know who was torn between voting for Hillary and voting for Trump. She wound up voting for Trump because a professional woman that she knew and respected voted for Trump, and didn’t buy into all the sexism accusations. But then she said “I would have preferred to vote for Michele Obama”.