Soft brake pedal

Hello from Australia ,

I have been having issues with a soft brake pedal ever since I bought this van.

My Holden/Opel Combo SB 1997 with C14SE engine has had a soft brake pedal so of course I bled the brakes but that made no difference.

I have done so far:

Replaced Front Brake Pads
Replaced Rear Shoes
Replaced Front Rotors
Replaced Rear Drums
Replaced Rear brake cylinders
Replaced master brake cylinder
Bled and replaced brake fluid like 4 times.
Inspect for leaks but there was none.

Does anyone have any suggestions on what could it be? Or is there a fault with the Astra SB? Should I upgrade to bigger brakes?

Please let me know.