The story I was told from Bitcoin developers was that it was done for code performance reasons. However, since the less-than check goes back all the way to the code's "Initial commit" [0], I'm not sure if that's fully accurate -- it might have been based on correspondence from the original author. At the very least, the misconception comes from Bitcoin's own whitepaper.

[0] https://github.com/bitcoin/bitcoin/blob/e071a3f6c06f41068ad1...