Question in Short:
Why is it that the terms valuable and invaluable mean almost the same thing while the terms famous and infamous are almost semantically opposite in meaning? That is, one is used to describe something/someone well known for their good qualities, while the other is used to describe something/someone well known for their bad qualities?
Question in Detail:
One of the answers to the question titled Difference between “valuable” and “invaluable” [closed] suggest that the term valuable is almost synonymous with invaluable, although the preferred answer points out their subtle differences as being costly and priceless, respectively. That is, something that can be bought or sold (valuable), as opposed to something that cannot be bought or sold (invaluable), yet is treasured.