The crowdfunding platforms bill themselves as just that - funding platforms. Once you raise on Kickstarter or Indiegogo, you're supposed to be able to take off like a rocket. The only problem with the story they sell you is that most startups don't take off, even after a successful campaign. You could say maybe they didn't raise enough money (and in most cases, I think you'd be right), but that still doesn't solve their problem - they raised what they could. If they couldn't raise enough money through crowdfunding, is crowdfunding really a viable option for hardware? And if not, why do over half of hardware startups choose to go that route?
On the other hand, maybe the horrible survivor rate for hardware startups is partially due to crowdfunding. After all, it allows companies to raise funds without being vetted in the same ways that a VC-backed company might be. Maybe it allows a lower quality of product/company/founding team through the gates, and as a result, we see a lower success rate for hardware.
The bottom line is I have no idea, but it's interesting to get a peek at the mechanisms behind "hardware is hard", rather than just falling back on the mantra and ending the discussion there.