The debt-to-finance-stock-buybacks can also be motivated by differences in corporate tax rate. For instance, Apple made this move some years ago, borrowing money in the US (despite having money outside the US) to finance stock buybacks. Repatriating the money and paying taxes would have been more expensive than the interest on the debt.

A lot of these monkeyshines were stopped by the recent tax reform, which brought US corporate tax rates down to levels comparable with most of Europe.