I've never met a reader who doesn't like short novels. Most people don't buy books by weight. If you do, you're reading the wrong article.

You will have to glean background, context from the few details you're given. You will not be able to doze and watch the scenery go by, or eavesdrop on extended conversations.For me, the opportunity to sit somewhere for two hours and read a book from start to finish–to submerge myself in it–is a thrilling experience. A short novel makes a straightforward demand: give me this time. There's no room for phone calls, feeding the cat, helping kids with homework. You, the reader, are expected to do some work.

There's no room for digression. No room for passenger writing. Every word is doing a job. So pay attention. A short novel is an event, not a trip.
What a short novel asks is that you commit, in one sitting, the same amount of time to reading as you frequently commit to a film, or a football match. Make that commitment and, in many cases, the pay off outweighs the investment.
The Old Man and the Sea, They Shoot Horses Don't They?, The Fox, A Meal in Winter, Animal Farm, Breakfast at Tiffany's, Bonjour Tristesse, Utz, Metamorphosis, The Fall, A Month in the Country, So The Wind Won't Blow It All Away... Jekyll and Hyde (a “sparsely-printed little shilling volume” as The Timeshad it, in 1886).
You'll already be adding others. But I wasn't thinking too hard, just throwing a few out there. In case you didn't believe me about that pay off.
Great short novels stay in the mind as objects, whereas, often, novels are ornate boxes with objects inside. Equally valid, but a different thing altogether, with a different mechanism of engagement. Simply put, with different rules.
It's a common mistake to believe creativity is about freedom. It isn't. It's about freedom within a given form. Rules are vital in focussing creativity into effectiveness, and generally the story itself sets them. A strong story will know whether it wants to be a long book, microfiction, a short story, a poem–even if it takes the writer some time to recognise it–and it won't let you make it into anything else.
Which can be a problem when the industry is obsessed with tagging books a certain way.

The Dig, for example, was the second part of a longer book for some while until it became clear it shouldn't be. It's around 28,000 words. Initially, the whole thing was 90,000 odd. I pretty much cut 60,000 words away in one feel swoop.

The reason it was 90,000 in the first place was because of considerable pressure to "write a longer book." For years after my first short novel The Long Dry came out, and even though it worked, length was the chief reservation from publishers. They wanted a "full length novel."
Well, as Beckett said, in response to criticism that his play Breath was short: “All of my works are full length, some are just longer than others.” It's extraordinary that the term "full length novel" still abounds.

If the novella exists, purely based on length, then the novellissimo must exist. The Count of Monte Cristo, Moby-Dick, War and Peace. Anything that will hold a heavy door open should be a novellissimo; anything that can be used to right a wobbly table, a novella.
And if we're breaking everything down into categories, then there should also be a distinction between a short novel and novella. Is it that the "la" at the end suggests frivolity, a lackadaisical, la-di-dah thing? Or is it that, in it's grammatical nature, novella is a diminishment? Whatever it is, I find it utterly impossible to refer to Heart of Darkness as "a novella." John Fante's 1933 Was a Bad Year, on the other hand, might be.
The nature of the term novella suggests something experimental, playful perhaps, travelling away from the narrative mores of a "novel"; the term short novel, in contrast, braces the reader for the narrative experience associated with structured history, emotional delivery, and–ironically–weight.
In the introduction to her brilliant "Year with Short Novels" at Open Letters Monthly, Ingrid Norton agrees:
“Fitzgerald's anxiety that Gatsby had been too short [“Remember this. Never write a book under sixty thousand words”] symbolizes everything that is tiresome in conversations about short novels (a term I favour over the more rarefied 'novella,' which implies a too-clear break between itself and the novel and thus invites vexing categorical hair-splitting). Too often discussions of length are concerned with publishers and awards, not with aesthetic merit.”
When it comes to the act of writing itself, you just have to forget labels exist and listen to the demands of the story. A good writer knows instinctively what they are doing, but are then required to explain it. That, I think, accounts for many of the laboured pigeon-holing terms, the vague attempts at category and so on.
Think of Steinbeck's self-determined "novel play" Of Mice and Men, (quickly termed by critics a play-novellette); or Dylan Thomas's Rebecca's Daughters, a film script that could be shot directly from the page–a slim piece of writing, in his own words, “ready for shooting, which would give the ordinary reader an absolute impression of the film in words and could be published as a new form of literature.”
What, exactly, are they? Other than exactly right for what they are.
Novel, novella, short novel? Ultimately it simply shouldn't matter. The only thing to be taken into account should be the impact a piece of writing has.