The St. Louis FED did a story on this last year [1] that basically said there are two main reasons why you would stockpile cash if you're a regular company (non-finance, non-utility): precautionary motive and repatriation taxes.

With respect to the first it comes down to uncertainty and credit constraints. Since the credit issue is basically zero for thees companies then it likely comes down to uncertainty in the market.

They want to be shielded in the case of a huge crippling depression or global catastrophe. Apple's "burn rate" is about 33BN a year, which means that 250BN would give them ~5-6 years to find a new market in the event of a nuclear holocaust if they kept spending the same with ZERO income.

At the same time, just like Venture Investors, they are all waiting for the next transistor level market shift to happen - whether they can make it or otherwise. So they are plinking away with small investments on projects that are high risk to try and flush them out.

Pick your poison:

Nuclear

Biotech/Genetics

Artificial Intelligence

Augmented Reality

Space Mining

Etc...

It's really about making sure that APPL will be around in the year 2200 irrespective of everything else.

[1]https://www.stlouisfed.org/publications/regional-economist/j...