As you've pointed out, the idea of travelling forward in time was more common to begin with than the idea of travelling backward. There were quite a few old stories about people who moved into the future, but the first story which involved a person moving back in time was Mark Twain's 'A Connecticut Yankee in King Arthur's Court', published in 1889.

As to why this type of time-travel wasn't written about before... that's an unanswerable question. Any attempt to answer it would be pure speculation.