There is another reason -- It's not to assist him in winning; it's to assist him in being a spoiler. This is what Virginia political science professor Larry Sabato had to say:
Twitter: Larry Sabato @LarrySabato The VP has to be an attack dog--but the ankle chomped is the other party's POTUS candidate, In this case, Trump's ankle is the target.
Picked her as a spoiler....
Guess what?? She will FAIL at that, too. Ms Snarly has more baggage than Imelda had shoes.