This is a truss system - when looking at the static load from the mast the front beam doesn't resist much of a downward force at all - The vertical mast load is carried straight through to the dolphin striker. The dolphin striker is then in tension to reduce the load. That tension on the dolphin striker then turns that load into a compression force on the main beam.

Pretensioning / prebending the main beam helps the entire system resist the load by returning to a neutral position when the system flexes.