All my published novellas are between 25,000 to 35,000 words. If you look at most how-to pages for novels and what word count will get you published, you likely won't see that number, because US publishers traditionally don't invest in the novella as a format. Why write a novella anyway?
Publishing is different in the Philippines. The reason why all my books are novellas? Because they were intended to be short. Printing over a thousand copies of each book is a considerable expense. My publisher gave me a maximum word count, so I had to learn to create a world, characters, and have things happen to them all in that space. I knew that each page should count. (They have since upped the max word count and I think it's evaluated on a case to case basis now.)
It's easy to finish writing one. That's the thing with focusing on just a main plot and a handful of characters -- you can write that fairly quickly, if you stick to a schedule.
It's easy to sell it, if you're self or indie publishing. You'll be able to competitively price a novella in a print or ebook store, and get a chance to be bought by people who are browsing for impulse reads.
People who don't regularly read might just pick it up anyway. I love it when I get this comment! Some college students I met recently told me that they preferred the novella because they can buy it, read it quickly, lend it to a friend, and talk about it the next day. Novellas are what got me started on reading, and I'm happy to return the favor by writing books that serve the same purpose.