SilverWook said:

First of an epic trilogy has been a gimmick on the covers of fantasy novels for decades now. I blame that Tolkien guy. ;)

Nah, you can't blame Tolkien for that. The Lord of the Rings is actually just one very long book, and was intended to have been read as such.

However, it was split into three volumes by the publisher, over Tolkien's objections, due to the cost of paper in post-war Britain. The only reason they even agreed to publish such a long story in the first place was because The Hobbit had been a success for them years before.