Why does a helicopter need cyclic control rather than just tilting the whole main rotor?
Tilting the rotor doesn't do much, in fact the body will be tilting more than the rotor. The gyroscopic effect will work against you.

The cyclic increases lift on one side of the rotor which will tilt the rotor. Which will then move the craft in the correct direction.

In other words the cyclic system gives a more direct response to input.