as in, because the microtransactions mechanisms already exist, and has been successfully monetized in other areas. The fact that news publishers don't use it (and opt for subscribers instead) is an indication that it doesnt work.
It could also indicate that the news "industry" has been utterly decimated and destroyed and defunded over the past 50 years and they don't really have the cashflow to play around and experiment with business strategies because they are desperately hanging on as it is and have all sorts of data showing them that they will never have the business they had 50 years ago no matter what because the simple reality is that humans prefer listening to a moronic talking head not ask hard questions over actual journalism anyway.
Empirically how? To my knowledge, there's never been a widespread micropayments system that targeted this use case. So how do we know? All we know is that publishers think micropayments would eat into their subscription revenue, and that they want readers to give them personal information so they can spam and track them (something that may not be possible with micropayments).
So how do we know this, empirically? I don't think we do.