Have to disagree on one part Jack,as i don't believe i am as bad as you say,"all" breeders are.
I also don't agree on reversing the surroundings to correct it. Far from as easy as that,but maybe we both witnessed different conditions.
My problem was noticed before 3 week & 3 week(ish) is my start to letting mum spend more time away,with gates locked. I always use bedding too.
As you said,a small litter don't help. Over heated pen & footing also.