Let's take an example. Computers can be programmed to determine the profitability of every customer in a bank based on the customer's current products, balances, and past performance. It is possible to go back more than one year to factor in trends. There is a lot of guesswork built in to profitability estimates. Return on investment is a backward looking concept, and can be determined with a great deal of accuracy and assurance.
Profitability is a forward-looking concept.
It is based on projecting future behavior based on the present and the past. It can be, and often is, wrong. It is subject to swings in the market. Usually missing from profitability calculations are such factors as the retention rate, the referral rate, the marketing costs, and sunk costs such as the acquisition cost, and the effect on behavior of various relationship building activities. For these, we must look to lifetime value.