I try to explain in another way:
Let's say your robot is at first 120cm away from the object. The sketch starts and it will stay in the first while loop (moving forward) until it reaches a point where it's 99cm away from the object. At this point the program leaves the firsts while loop. The following block stops the motors. The program logic now checks the condition of the second while loop, which is not matched as the current 99cm is more than the 80cm the while loop expects to be run. The program checks the condition of the third while loop which is also not met, so the loop block is not executed. The end of the loop is reached, so the routine starts from the beginning. None of the while conditions is met, so the only code block that executes it the stop of the motors.
Do you see why you robot stops at 1 meter and won't move anymore?