This is most likely due to a few key settings that are not enabled. These two settings are called Automatic Network Connection and Network Preference.

• Automatic Network Connection tells your device to connect to this network whenever it is in range without the user manually selecting it or entering the password.
• A preferred network will be prioritized if there are other networks that are in range of the Chromebook. 

The attached guide will show you how to access and manipulate these settings.