Can you imagine a bachelor getting voted in as president? Neither can I:
It would be very strange to have a president with no first lady. Really strange. I think it says something about a candidate for president that they’ve taken care of certain things in life, like getting married, having kids, buying a house, and pursuing their career and excelling at their career.
So he can make jokes about rotating First Ladies all he wants, but when it comes down to it, the fact that he is still a bachelor will be a big deal to people, especially when there are other married alternatives that in most cases are much better candidates.