Software is unique because it can be copy pasted. A builder that makes a house in 4 months the first time might estimate 3.5 months for a near identical house. But to deploy the same desktop app on two computers you merely reuse the installer from the first computer, and to recreate the same page in a different app you can copy the code, so no one ever estimates doing the same work twice. Every software problem has at least a little novelty, because if it isn't at least a little different, the work is already done.