GCP is far superior to AWS in almost all ways. It's also probably 30% less expensive on list prices.
Apple aren't dumb. iCloud is terrible because web engineers know Apple can't do services as well as Google, so why not go work at Google instead? This way, a familiar platform is available and they can start trying to recruit those people.
As for any perceived security issues: it's highly unlikely that the FBI has a tap into Google's network. The NSA might but that's irrelevant since they tap everything.
GCP is actually super secure in the sense that all data is encrypted at rest. As long as Apple follows best practice in only communicating over HTTPS/TLS, this is no less secure than Apple's own DCs.