Why do women have back pain associated with large breasts?

My husband brought this up resently and I couldn’t think of a good answer. It seems that the average healthy woman should be capable of building back muscle that would acclimate to her breast size/weight?

I have terrible back pain and I know most women with large breasts do too. For the record, I am a natural 32DD and weight 125lbs at 5′6. I have excellent muscle strength. I tend to believe it’s because the weight is constaint so our muscles do not have a chance to recover and consequently adequate muscle cannot form.

Just curious what you all think.