Your mundane explanation misses the main point that perfect security can't exist while maintainint function. It is not just a matter of cost cutting, it is a (sort of) fundamental law that security and usability are opposite ends of a spectrum, at the limit any gains in security can only be achieved by a loss of usability. So any system that is perfectly secure will be perfectly unusable, or in the business angle, any system with 0% fraud will have 0% sales.