Apple and Alphabet are very different companies. I know Apple has previously taken out an incredible amount of debt via corporate bonds due to it being cheaper to pay tax deductible interest than actual taxes.
++ This has a lot to do with it. Apple has repeatedly issued bonds to generate cash locally against cash/investments held overseas in order to avoid the tax liability that comes when you repatriate foreign holdings. Apple has just done this to a much greater extent than a lot of other companies, and uses this debt mostly for stock buybacks.
There's nothing even remotely under the table about what Apple does and they certainly have the credit to do so without any long-term risk. It does, however, poke a hornet's nest of criticism that what Apple is doing is a particularly aggressive way to avoid paying U.S. taxes, with the result only benefitting large institutional investors. But that's an argument for another thread.