Motivation for frequent key updates
All block ciphers leak information.  No matter the mode used there is a limit on the amount of data that should be encrypted with a single key, irrespective of the number of different IVs used, in order to not leak too much information that an attacker might be able to determine some of the encrypted data.  For AES, it seems that the limit seems to be around 64 GB no matter the mode.

See the book Cryptography Engineering: Design Principles and Practical Applications and the paper The Missing Difference Problem, and its
Applications to Counter Mode Encryption.