Because the SV VC business model isn't to build a traditional profitable business that beats the competition by providing a superior product/service for a competitive price. It is to dominate the competition by subsidizing the real cost to consumers, until you have taken over the market and can raise the price and lower the quality of the product/service.

Edit: Or the business model is to be acquired by a FAANG who fears they need to get into your area and care more about optics to their bosses/shareholders than how financially sustainable your startup is.