Why would anyone put so much time and money into an activity they hope to lose?
I think the whole issue was created to make him look bad. "Hey, if you lose, will you accept the results?" After Gore/Bush, I don't know if anybody would immediately say "Yes" without thinking about the possibility of questionable things happening. Would you accept the results of an election with fraud? Until the election happens, you can't have 100% confidence that you won't think there was some fraud.
A lot of us here have questions about voting machines, people voting who shouldn't, etc. These are natural concerns that should be Hillary's concerns (as they are now) and not just Trump's.
The question was not "Assuming there is iron clad proof of no voter fraud, will you accept the results if you lose?" The answer would almost certainly have been "Yes" in that case. I think all of us on this site are smart enough to assign non-zero probability to the chance that this question was asked WITHOUT the "no voter fraud" disclaimer specifically to elicit the reaction that it got.