Because the authors are Italian?

Or because the funding came from espresso product manufacturers?

Filter coffee catches oils and particulates, so it's better to try using espresso in case some of those compounds are being removed.

Unless the filtered compounds are causing/preventing another deleterious effect.

Indeed, but if you have to choose a subset amongst the gigantic combinatorial space, the biggest one is probably the first you should choose without some better reason.

Likely cultural factors, but clearly this extends to other methods of processing coffee.

Another recent study found that coffee brewed with a paper filter reduced the chance of type 2 diabetes. That did not happen with espresso or other coffees brewed without paper filters. The explanation offered is that among the coffee compounds, one protects against diabetes and another counteracts the first. A paper filter seems to capture the second compound letting the first through.

Perhaps you need espresso filtered through paper to get both benefits? ;)

Don’t joke about it, it’s a real thing! You can get paper filters in espresso portafilter sizes, and some people use them under the coffee puck and some above (to distribute the water more evenly to try and reduce channeling of water through the grounds).

It's reasonably common for people to use aeropress paper filters in their portafilters. But I think more people who use a screen opt for a metal one.

Not necessarily true, espresso extracts more compounds from the coffee than other brewing methods.

Not necessarily true, filter extracts more caffeine than espresso at the same soluble extraction levels:

https://www.youtube.com/watch?v=etnMr8oUSDo

The truth is there is not enough scientific research to compare all brewing methods. Espresso uses high pressure but very short brew times, but filter uses more water and longer brew times therefore the coffee comes out totally different, and that's before we even talk about different grind sizes and roast levels.