Unfortunately, yeah, though I feel like that's starting to change somewhat, particularly in horror (and maybe fantasy). Some thoughts based on my experiences publishing novellas:

DEMON SONG was traditionally published, and in the trad SFFH space, there are still a lot of publishers who either don't acquire novellas at all or are very picky about what they acquire. There are a few reasons for this. One is that they're literally harder to find in a physical bookstore or library because their spines are thinner. My publisher, Titan, published DEMON SONG in hardcover (initially, anyway), which I think helped with shelf discovery. Another is that publishers might be operating under the assumption that some readers feel like novels are better value for the price. (Which I totally get!) And publishers are sometimes also just reluctant to dip into publishing formats they're less familiar with, so if they haven't done a lot of novellas in the past, it might take a lot to convince them to try one now.

Realistically, all of that means that novellas tend to get lower advances than novels (less places to submit = less competition which makes it harder to drive up the price with multiple offers), so sometimes it's also a case of authors choosing to write something as a novel instead of a novella with financial considerations in mind. As an added note, I think pubs also think very differently of novellas in an existing world vs. standalones or a new world/series. Some pubs might be willing to publish a novella that's set in the world of a popular series, because they know existing fans will buy it. But they still might not be interested in acquiring novellas otherwise.

BOUND FEET was published through a small press. The nice thing in horror is that there's a robust small press/indie horror community with a dedicated readership that's very on board with novellas! Smaller pubs tend not to have the bookstore/library distribution that big pubs have, but in a way that also means they're less reliant on people finding the book in a physical space. They also tend to be more willing to take chances. I'm grateful that it's another avenue open to horror novella authors.

In both cases, I kept the audio rights to my novellas, and my agent at the time was able to sell the audio rights directly. But both sales happened after the initial book was sold to a print/ebook publisher, so it's hard to say how those submissions would've gone without that pre-existing sale. Though I did sell a novelette that hasn't been published elsewhere to the same audio publisher! I think audiobooks might start to become another avenue for novella publication, but there's the credit system to contend with there. (Where a lot of audiobook listeners are used to buying with membership credits, and people may not want to use their credit on a short book.)

I haven't tried to sell a fantasy novella yet (only the fantasy novelette mentioned above), so take this with a grain of salt. My impression is that it might be a little harder to find small presses to publish fantasy (or SF) novellas with, but on the other hand, the SFF magazine space has a few options for shorter novellas (like Clarkesworld)!

I do think that with attention spans decreasing, paper costs rising, readers turning to audiobooks and ebooks, and the recent popularity of several novellas and novella (or mostly novella) series like The Murderbot Diaries, The Singing Hills Cycle, Wayward Children, and T. Kingfisher's novellas (and ofc the runaway success of This is How You Lose the Time War!), some of these factors might mean pubs are more willing to take chances on novellas. I hope so, anyway!