Back in February 2016, there was a long, drawn out, and very public dispute between Apple and law enforcement agencies, where the Cupertino firm was asked by the FBI to unlock the iPhones owned by the San Bernardino shooter. Apple's response was that iPhones are encrypted and it said that it wouldn't help.
What doesn't use end-to-end encryption, however, is your iCloud backup. And as it turns out, at least according to a report from Reuters, that's only because the FBI complained about it. Apple decided that it didn't want to "poke the bear" again.
Not having encryption on iCloud backups makes life a lot easier for law enforcement agencies, as they wouldn't even need access to your iPhone to find out what was on it. Presumably, Apple only turns over this data with a proper warrant.
Apple has long boasted being a champion of user privacy, from the public dispute over the San Bernardino shooter's iPhone, which ended in the FBI having a third-party break into the device, to posting an ad at CES in Las Vegas that said, "What happens on your iPhone, stays on your iPhone". It would seem that this is only the case when the company is in the public spotlight though, as its actions tell a different story behind closed doors.
The firm did plan on offering end-to-end encryption on iCloud backups at one point, but those plans got scrapped. Aside from push-back from the FBI, it was also decided that consumers would be more at risk of losing their data. Once you lose a password to something that's encrypted, it's gone forever, as not even Apple would have been able to access it.
Competitors like Google Drive and Microsoft's OneDrive do use encryption to store all of your stuff, however the latter is clear about how it handles cloud data. Presumably, those companies are under the same pressures as Apple.
According to Reuters, in the first half of last year, Apple handed over full device backups for about six thousand devices in 1,568 cases. For U.S. intelligence court orders in the second half of 2018, the company handed out data from over 14,000 accounts.