In my experience the HN crowd is generally interested in cutting edge science that is relevant to pop culture.

Ever since cannabis use has become normalized there has been a vigorous debate about its long term safety and the issue is far from settled. This study is another data point that we as individuals can use to make decisions about cannabis use.

You are right that in practices we can't just look at cannabis use in isolation from the rest of a persons lifestyle. However, science almost never starts with a comprehensive analysis. Instead it starts with smaller targeted studies that are then used to build the comprehensive arguments.

So while yes I it would be more useful know the risk of cannabis use relative to drinking alcohol, consumer sugar, lack of exercise, etc... this data point in an of it self is still useful.