Only viewing total cost misses the point. For some people, it may be more reasonable for them to want to pay a fraction of the cost monthly vs. one big sum ever

Only viewing total cost misses the point. For some people, it may be more reasonable for them to want to pay a fraction of the cost monthly vs. one big sum every 12 months. $10/month is more expensive, in total, over a year. However, $100 is more expensive in the short-term. Also, paying monthly is only more expensive if the person paying decides to stay that long. Monthly payments allow flexibility to cancel rather than committing to a year.