Do you have the "pay grade" to be able to make this assertion credibly? One cannot, in general, see the forest for the trees. This adage is not merely a put-down.
However, I was an Assistant Director (which is a senior tech / middle management kind of level) at first an intelligence agency, and then at a similar grade in a law enforcement organization and then later a security engineer at Google.
The idea that an intelligence agency (or law enforcement agency) would ask Google for help isn't far fetched, in fact when I was in law enforcement we'd ask private companies for help all the time. Some of the time they'd help, the rest of the time they tell us to come back with a warrant.
Google was famously in the second category, to the point where we'd not even bother asking. Even if we had a warrant we'd hesitate because we'd expect Google to challenge the warrant in court and it'd be a huge expensive hassle.
When I worked at Google it was the same, the idea of sharing private information with anyone was anathema. Engineers even being able to see private information without an audit trail and alarms going off was next to impossible.
The idea of a secret extra-legal conduit of information from Google to the US Government seems so far fetched to me that I have trouble even considering it. If there is a conduit for information it's there because the US Government has some legal instrument to compel Google to create it and that Google grudgingly has accepted the instrument as valid.
But what do I know, like I said, I wasn't the CEO of Google or DIRNSA. Maybe I just was never in the right rooms or policy meetings? Maybe everything I saw was staged for my benefit.
In reality, the explanation was even simpler: in the US, authorities either didn't bother asking, as you said, or put the effort in crafting a proper request.
Elsewhere, they assumed they could obtain anything (or remove anything about a local figure), just because they had a badge. In some cases, the requests were so ridiculous that they had to be educated about how the law worked in their own country. Over time, compliance increased in those countries as well.
It's also an open question how much data Google is compelled to share by law in the age of NSLs.