[/nq] I believe the period got moved inside the quotation marks regardless of whether it made sense back when lead type was hand set. The period was a tiny, thin piece of type and if it had only a space after it had an unfortunate habit of getting broken off between the type stick and the press. Most often by the rag used to clean the type in the galley or even once the page had been locked into the chase after proofing.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.