RealityTVWorld sums it up pretty well:
On Tuesday night's most recent episode of the reality dating series, less than 1 million viewers reportedly tuned in, which makes I Wanna Marry "Harry" the lowest-rated original series ever on any of the Big Four networks -- Fox, ABC, CBS, and NBC.
To be fair, the show followed the same premise as most reality shows - put some girls together, let stuff get catty, have girls magically fall in love with a mystery person they've just met even though the person is probably hooking up with many of them, etc. Also to be fair, I couldn't sit through an entire episode without getting bored. So I guess that's why the show failed - it really wasn't good.
At least the women got their little slice of fame, and if we really want to know who wins the fake prince's heart, the episodes will be on On Demand, Hulu and other places.