For a while it was rational, in a strange way, to not try to be profitable on a sale pur sale basis. Investors are dealing with a zero rate environment where they're looking for long term growth rather than short term profit. As long as money was cheap, and silicon valley investors were telling themselves that they could build the next world conquering consumer tech firm,. In the next funding round, the best way for a start up to make money from investors was to lose money acquiring customers.