The iPhone 5C addresses no market so it's not too surprising to see it floundering.
I think it does, but it's the opposite end of the spectrum than what most people wanted it to be: The iPhone 5c is for rich people. They can afford to buy last gen hardware because they'll simply buy a new phone when they start to feel it. They're also the only people who'd care about the colours. Someone who's strapped on cash would be insane not to buy the 5c and wrap it in a colourful case instead, as a long-term investment.