I know there's a cold boot attack for Android called FROST (Forensic Recovery Of Scrambled Phones). But there doesn't seem to be one for iOs. Why is this? Is it because iOS is inherently more secure and more resistant to such attacks? Or is it simply because no one has bothered to write an exploit for the iPhone because they can get the unencrypted data from the cloud?
The attack simply does not work on iphones. Main reason being iOS performs key wipe on the RAM, so it is not possible to retrieve any key via cold boot attack. You may find this link useful. Note also that this attack was based quite some time ago on Android 4.0