I cannot speak for all, but for me, my lack of lower back flexibility is beyond " just being tight". I agree a loose (i.e. weak and soft ) anything is not good. But, my lower back has gotten to the point it is limiting my activities - Chronic inflexibility. Something needs to give. I know, I know, JUST SQUAT MORE, right?
When a person reaches beyond the limits of their ability; they shall they make progress. There is no other way.