If they're not a highly-valued (ie speculative) startup, or one with a CLEAR PATH TO PROFIT, why the fuck would/should anyone be investing in them?
It is called the "the greater fool theory". It is investing in a venture even after knowing it has no real prospects, investing in ponzi schemes knowing well it is a ponzi scheme etc. Basic idea is, "yes it is a scam. I know it is a scam. I might be a fool to invest in this thing, but, I will flip the investment to some greater fool before the whole thing comes crashing down."