There are cost/benefit ratios for tangible direct costs, tangible indirect costs (e.g. cost of maintenance, cognitive load, opportunity costs), and a wide array of intangible costs, most of which are psychological factors which are often disconnected from, even opposed to, material benefit.
And purchasers rarely manage to acknowledge even a significant fraction of those costs, much less take them into account.
That's why we have behavioral economics. Some economists finally admitted that people are not rational economic actors.