The counter arguments that I've seen (there may well be others) are either that it does see those opportunities, but not at this precise moment in time, so is keeping the cash for later. At the level of $156b, this seems a bit unlikely but hey maybe they have some great ideas in the pipeline.
The alternative is that they don't but aren't distributing it to shareholders, because of the tax implications of that distribution (and in general many corporations seem to favour buybacks rather than dividends for tax reasons), and they have some hope that those tax implications will change in the future (or their share price will fall, allowing for better buybacks), allowing them to then distribute the money in a way that benefits the shareholders more.