Why does it seem strange to you? my guess? because it is not what you are used to. Just as a crapper flushing in reverse when you change hemispheres seems a bit strange the first few times.
When the professional standard come about? hard to say. Linus Yale patented the modern pin tumbler lock in 1868. Not much has changed in basic design since then, except quality control. Originally materials and consistancy made the springs fail on a greater rate when mounted upside down in the beginning. Today, springs fail less and therefore, having a lock mounted upside down is less of a liability.