Because it is important: While WhatsApp instant messages benefit from end-to-end encryption, your backups stored in the cloud do not. That means accessing your chat backups, either nefariously or through a court order, would grant access to your private message history. However, users who have been testing WhatsApp on Android now have the option to enable backup encryption, which makes their backups and messages more secure.
The advance security feature is available in the latest beta version of WhatsApp for Android (184.108.40.206). When activated, both the chat and media history in your cloud backups can be protected with a password. However, this comes with a downside: if you lose your phone and forget your password (or 64-digit recovery key), it will not be possible to restore your backup.
Your backup password is saying to be private and not shared with WhatsApp, Google, Facebook or Apple. It can only contain lowercase letters and digits, and if you lose it, WhatsApp can’t help you remember it.
You have to balance that warning with the knowledge that if your Google Drive (or iCloud Drive) is compromised in any way, your WhatsApp chat and media history will be safe.
We hope that WhatsApp will roll out this feature to more users, including iPhones soon. For now, it is available through the Google Play Beta Program in the WhatsApp beta application for Android and, as always, also in our Downloads section.