No one builds a system to fail, but failures do happen. A good design is one which incorporates a high level of fault tolerance.
Redundancy is a key element to achieving that level.
Having three diverse Internet sources, Green Apple can maintain Internet availability in the event of loss of service in even two of them. With respect to network performance, bandwidth plays a critical role. You cannot send the traffic of a four line highway suddenly through a country road without causing delays. The same applies to Internet bandwidth. If an ISP wants to avoid bottlenecks, they must have an appropriate amount of bandwidth to support their traffic.