Accountable is interesting - they are as accountable as any other company, and if anything, both are under much closer scrutiny than anyone else, and have bigger reputational risks than anyone else.
People say this a lot, but why does nobody care so far?
I'd posit the simple answer is "it's easier not to", but also that governments are happy to reinforce a duopoly they control. We already know both Google and Apple are PRISM members as well as involved in the international FIVE-EYES network. That never really stained their reputation, despite being a universal backdoor. Google has exploited and broken YouTube several times over, but nobody stopped using it in objection. Apple moved their servers into government-owned Chinese datacenters, and nobody protested it financially.
The threat to their actual reputations is almost non-existent, from what I've seen. If people cared, we wouldn't be fixing FAANG's problems 10 years after-the-fact.