Stretching 1 brake line = no stopping

Just finished replacing the right front upper control arm with a cognito from their leveling kit. Needed to drive it before I had time to do the left. While driving, the brake pedal was intermittently going to the floor with no braking power. Yes it was a holyshit moment! Brakes were working fine before and there were no leaks anywhere and master cylinder was full. Pumping the brakes would firm up the pedal and bring it back to functional. Did some more test driving and figured out the pedal was going soft after hard right hand turns. So I turned hard right and had a look at the right wheel. The brake line bracket was messing up the routing which was causing the flexible rubber line to be stretched tight and possibly even pinched closed. Obviously I need to fix the routing so the line doesn’t get stretched. But my question is why would 1 of 4 lines getting stretched/pinched cause the pedal to go soft and lose braking power to all 4 wheels?