Occasionally there may be extenuating circumstances and if so, it becomes readily apparent and things can be sorted out.
I have never had it happen.
There are few scenarios I have heard about that play in. One that I doubt plays in here is that the other person got cold feet, usually due to a red flag. It is women that do this one. There is something that they suspect like the guy being married, an alcoholic, an abuser or something.
The second is that the person is married and can't get away, got busted or something.
But the most common one is that they knew enough about you such as the car you were driving and what you were wearing. They lurked near the meeting site, didn't like what they saw and blew the whole thing off. I have known both genders to do this one.
A friend of mine did that once. I asked him how his meet up went and he said she was ten years older and fifty pounds heavier than her picture, so he just pretended he was somebody else. Why a person would lie about something people can see with their own two eyes is beyond me