Why does your brake still go straight to floor you have changed master cylinder power booster and bleed the brakes many times?

Most likely that you still have air in the lines. Make sure the brake pedal is held down until the bleed screw is tightened back up between pumping and bleeding cycles, otherwise air will be sucked back into the system.

pump brake pedal until there is pressure

hold pressure on pedal

loosen bleed screw ( air or fluid should come out and pedal should go to floor )

hold pedal to floor

tighten screw

pump pedal again

repeat this for all 4 wheels and until only clean fluid comes out.

The pedal should get better as you work through all the wheels.