Increased interaction does have value because, as mentioned in the article, it keeps users coming back to the service -> more likely to find it useful -> more l

Increased interaction does have value because, as mentioned in the article, it keeps users coming back to the service -> more likely to find it useful -> more likely to use the paid service when their trial ends. The two metrics given as examples are just that - examples. Various other more "bottom line" orientated metrics like which user account types interact the most, how often they return before the trial ends, are also being measured. However, it's not all about "bottom line". The second of the two metrics doesn't tell you anything about how much revenue is being generated - as is explained, this is to help find out which fields users are requiring additional advice so they can potentially improved. Measuring the "bottom line" is important, but it's not important for every single metric.