Why Estimating Accurate Cost For Custom Software Development is Difficult?

The question is that of how custom software is something that one creates from the ground level and not much like buying a computer which is a basic product. So this is project compared with the product, is where the answer is that the customizations that one wants in the software will ultimately balance is cost. Building custom software is like making a custom home and actually choosing everything you want to as compared to the cookie cutter homes where with certain specifications are chosen and all the houses are made. It is, hence, very difficult to quote a price for a professional as to how much building custom software would cost.