Hi,
Hm that is because of process called "frustum culling". Basically everything what is outside of camera view is not rendered at all to save resources and computing power. Since that objects are not rendered they can't cast any shadows. Using frustum culling makes huge difference when it comes to performance, so I would advice not to disable it even if that is possible.
Maybe baking lights may help in this case? I'm not sure because I'm not experienced with this topic, that's only my guess.