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.