Gradient inks do not flow across multiple objects by default. In order to accomplish this, use the Vector Gradient Tool.  

The Vector Gradient tool applies the gradient ink that was used last or that has been defined as the default ink.

To flow a gradient ink across multiple objects, shift-select more than one object. Using the Vector Gradient Tool, drag across the selection to apply the gradient flow. The same can be done with groups of objects and text objects.