Not every study has to be about everything, there’s plenty of interesting things this tells us.
Lots of follow up studies too, are gen z women the same or do they all go for older guys or the same guy? Is this trend tied with sexual identity, how do men feel about it, do porn habits correlate, how does it split demographically and economically…
Doing a study on all these factors would be huge and expensive, getting a good data point to inform future study design is a vital step.
But yeah look up the paper I bet they asked more than one question and have a methodology based on sound principles trying to increase understanding of a complex subject.