Imagine if I had two friends, Google and Yahoo. Both are asking me if they can borrow a dollar.
Over the last few years when Google borrows a dollar it gives back an extra 3.5 cents the next year as a thank you. On the opposite side, when Yahoo has borrowed a dollar they've lost 13 cents within the next year.
Left to their own devices, Yahoo will implode and be out of money in under 7 years, likely much sooner. The $4 billion price tag was a way of salvaging what may still be valuable properties within Yahoo, but the company on paper is rapidly losing money at any valuation.
It's like asking someone to buy a car that's broken when it's unclear if they can fix it.
Also, at this point, under-investing in security never pays.