Why React native navigation loads all components at the same time?

I am using react native navigation v2 by wix. I have a welcome screen with login screen and register. I start the startAuth.js from App.js. There are two tabs with login and register.

But as soon as app starts the componentWillMount methods runs in the register screen but yet i am at login tab.

Why is this happening?

react-native-navigation's Tab does not support lazy loading. But there are two special lifecyle functions where you can put your logic when component appear or disappear on screen

• componentDidAppear(): called each time this component appears on screen
• componentDidDisappear(): called each time this component disappears from screen

https://wix.github.io/react-native-navigation/docs/screen-lifecycle

There is also a discussion about topic https://github.com/wix/react-native-navigation/issues/1250