There is a weekly limit for the amount of protected and unprotected resources the main account can loot, and each resource type has a specific load.

However, it has its unique way of calculating it. For example, stealing 1 million of fuel won't deduct the same amount from your weekly limit; it will also add the specific load for this type of resource.
So, if you can't steal more resources, please wait until next week, when the limit will refresh.