A recent Variety article pondered the question as to why all the Oscar nominated shorts this year were from countries other than the United States.
"Easy answer: Voters just didn’t find any American-made films worth including. The more complex answer: foreign-made films are often heavily subsidized."
As someone who has participated in the Oscar short film nominating process for almost two decades, and has probably seen over 3000 short films in my life, I don't think that the budget of the film has anything to do with whether the film is Oscar worthy or not, and budget is never a consideration in voting.
The real goal of the nominating committee, which usually screens around 120 live action films per year, is to pick the ten films that make up the short list from which the final five Oscar nominees are selected.
In my years serving on the committee, I have seen huge budget shorts (often from America) with big stars not get nominated and micro budget indies with unknowns make the list of ten. Why? Because budget has nothing to do with the judgement on whether it is a film worthy of an Oscar.
More to the point, the personal questions each voter asks him or herself, during this nominating process are things like, does this film move me? Is it about something? Does it follow through on its premise? Does it land the ending? (Many potentially great short films frustratingly fail at the ending.)
And most importantly, Is Oscar-worthy filmmaking?
Typically filmmakers from other countries seem to be dealing with more complex subject matter, whereas, in my experience, American filmmakers seem more drawn to doing films inspired by (copied from) bigger studio fare. If I see another short film ripoff of Raiders of the Lost Arc... This is not always the case, (there are good American films) but often it is.
International filmmakers tend to have a more original voice and take more chances than their American counterparts. This tends to mirror the state of filmmaking in the world.
So the reason there were no American films selected for the honor of an Oscar nomination this year, is because in the opinion of the Academy voters, the films from other countries were more exciting and engaging. (Of course this represents my opinion and not necessarily that of the Academy... )
The takeaway for American filmmakers?
Be bold! Take chances with your films! Show your voice as a director! As Judy Garland was fond of saying... "Be a first rate version of yourself and not a second rate version of someone one else."