Toyota and others have gone to chains several years ago in many of their models. According to local motor component subcontractor engineer, it’s strictly an engineering decision that is only indirectly related to the cost of making the motor. It had to do with the motor’s overall performance and planned life expectancy.
The initial move to belts may have been for quietness but with the advent of variable timing and their varied approaches to increased efficiency and power and along with other such technologies the decision was made. It is not a simple, “which is cheaper/quieter” that the average consumer can only guess at. Maybe increase stress; who knows and it’s only a guess for we non engineers.
The chain in modern day cars is no more of a durability issue than a connecting rod for a non OHC motor. All internal parts that are not routinely replaced or serviced are engineered for compatible life expectancy by each manufacturer according to this engineer. Theoretically, a chain can be made to be the longest lasting component.