I hear the phrase “hardware is hard” dozens of times a week. 
  Repeating this cliche misses both the point and the opportunity. 
  If we want to live in a world of autonomous cars, consumer space travel, 
  and a green energy grid (I know I do) we have to stop defining hardware 
  by its difficulties. The truth is, it has never been easier to start a 
  hardware company. Why is this phrase so common?

Because hardware requires more rigor and process to handle correctness in its implementation than software does because the iteration cycle is longer and more expensive than just pumping a PR into a CI pipeline, and people keep getting the advice when starting a new company that they should avoid applying any engineering rigor to their development cycle for as long as they possibly can because it's supposedly a giant waste of time until after you've got your product-market fit sorted out? Perhaps?

So in that vein, "hardware is hard"(er) because what counts as "minimally viable" is a more strict and higher bar than what people have been incentivized to create with software.

Or at least that's the impression I get from people when I hear them say, "hardware is hard".

I didn't find the Hardware Myths section very convincing, because it keeps comparing B2C products (fitbit, gopro) to B2B businesses (SaaS). Scaling business customers is always going to take longer, hardware or software.

I think the advancements in contract manufacturing covers most of what makes hardware easier today.