I think the problem with hardware startups is more subtle. Unless you open up a fundamentally new market segment or find a niche application, your product is asking to be commodified. Smartwatches and fitness trackers were too obvious a category and Samsung, Apple, etc. were sure to swoop in and win. There really is no distinguishing feature for Jawbone or Fitbit. Other hardware startups like Anki are doing stuff that's niche and novel in areas unlikely to be ever entered by Apple/Google/etc.
The technology component of Jawbone or Fitbit was, even in 2007, very very basic and hardly novel. There is literally nothing in Jawbone or Fitbit that is super novel: their sensors aren't ground breaking, their algorithms are (presumably) meh, etc.
VC's hope that these companies will mature to become superstars and achieve the level of tech quality of Qualcomm, FB, GE, Intel, Google, etc. in their respective markets. This didn't happen with Jawbone or Fitbit.