while i'd share you sentiment at emotional level, at practical level lets be just toward the VCs. They don't have the scale of money to invest into "building devices to help people walk" - to reach the stage when it can be sold (ie. FDA approved, blah-blah-blah, and without that your device would just not be able to reach the majority of the people who would need the device) it would take not millions, at the best case scenario it would take high tens of millions.
On the other side by financing "a location-based restaurant recommendation app" the VCs' millions help to generate super-wealth which can take on the next scale challenges - look at Musk for example. Unfortunately, there aren't many Musk-s around (honestly i don't undestand why whouldn't Brin or Page or Ellison do something like Musk, they even have much more money than he does (he is even not that super-wealthy, more on the lower side of the range))