To prove their valuation and get a stronger hander at the negotiation table. Many companies raise money not for capital investments, but for:

a) create news and get free PR (press loves such eye-popping numbers)

b) get higher valuation numbers that will motivate the employees more (they have the stock options after all)

c) get more powerful/influential shareholders who will help clear the hurdles in the company's way

This is not exactly how capitalism is supposed to work - capital has to be used judiciously to build future growth.