As with others, I think your assertion is incorrect. Based on an analysis of the 342 film title given in this list of film releases in 2019, I find that 26% of films have 1 word titles, 32% have 2 word titles, 19% have 3 word titles, 13% have 4 word titles, and the remaining 10% have 5 or more. The longest was 9 words.
This shows a strong preference for short titles, which are presumably more memorable, but not a dominance of one word titles. TwoInstead, two word titles are the most common, and. 20% of the film titles began with the word 'The', and of these 28 (8% of the total) were of the form 'The X'.
I can see no discernable pattern to the 89 one word titles, there's no obvious predominance of names, places, verbs, objects, times, emotions, etc. but rather a mixed bag of pretty much every type of one word title you could think of.