As to why everyone is chasing unicorns, one of my friends who's actively trying to get funding for his hardware startup sums it this way: VC's would make more from 1 unicorn than 50 other mildly successful businesses, and the other 50 businesses would probably require just as much work as the unicorn.
Its a really fucked up calculus to be sure. I'm not sure what the solution is though. How do we encourage VC's to invest in more meaningful startups?