That's not always true. Ergodox-ez.com has an awesome product (a keyboard) they funded through indiegogo. Not to mention basically every 3d printer company, even the VC funded ones.
Crowdfunding (and pre-ordering in general) helps hardware startups raise the cash they need to manufacture a batch of product. Without it, they'd have to raise the full cost of the batch in advance, (which is probably a lot,) on the hope that customers will buy it up. I can't think of many startups that have that much goodwill from investors.
It makes sense to be extremely skeptical when giving your money to an early-stage company, whether as an investor or a pre-order customer. But writing off crowdfunding in general means you're writing off almost every hardware startup, including some of the great ones.
What I do see is they use an open source firmware, used on several other keyboards.
First responder to this thread was pretty much lambasting all projects that opt for the crowd funding pathway, which I think is a grossly unfair judgement call.
I don't think its unreasonable that someone who takes a risk on giving you money in your infancy to realise your product should get some equity or something else from it that's more than just a "preorder".
People should avoid startups those use crowdfunding websites as risk free capital gainer preorder pages.
They don't get proper investment for a reason.