I think the long term trend is less about fashion than word processors with grammar etc making longer works more viable. They just assist longer works far more than short ones.

Let’s say a word processor saves 1 minute per word in the writing/editing process over a typewriter as you’re not messing with paper, ink, and moving stuff around, or thumbing through a thesaurus etc. I am not saying it’s always constant round number just that it does provide some automation that’s scaling with the number of words.

For a short poem it’s handy, but not that critical compared to inspiration etc. But our hypothetical 1min per word adds up to a sold month for a 120k word and a full year for a 1+ million word multi part epic that’s going to make many projects more viable. This becomes more pronounced the less effort per word people are putting in, which opens the door for someone to entertain a small group of fans with lots of low effort words on Patreon etc.

Notably word processors have been around for decades, but there have been a steady drop of improvements over time. Writing a novel on your cellphone isn’t an ideal work environment by any stretch, but it fits some people’s lifestyles very well etc.

Edit: Not that you can’t find people writing short stories on Patreon, but it’s easier to hook people on advanced chapters of a work. And after its written publishing on Amazon is so easy even a few sales make the effort worth it. Thus a flood of longer written works showing up.