>It is also inherently insecure

How is it inherently insecure when it provides encrypted chat?

Defaults are a powerful way to influence user behavior and there is good reason to have the chat not encrypted. It facilitates quick searching of keywords which for many chat users is an important feature. Many people chose to write things down or have discussion in text so they don't have to remember.

If users want E2E by default they are free to use another service or just coninually use Secret Chat.