If I am not mistaken, the US is asking for the data stored in iCloud. If some of that data is protected by E2EE and if Apple doesn't have the encryption keys, the US gov't can't do much with that data, unless they are able to break the encryption themselves. All they get is an encrypted blob.
The UK is requesting Apple to provide a backdoor to defeat their own encryption. This is bad on a completely new level. Not only is this infinitely more intrusive, but it would also create a channel that can - and will, eventually - be abused by cybercriminals.