To answer the question raised by the title of this post I looked at the data on BoxOfficeMojo.com for this century to determine the share of the year’s box office gross accounted for by the ten highest-grossing films.
In the decade 2000–2009 they ranged between just over 23 and just under 27 percent of the total, and averaged 25 percent over the whole decade.
In 2010–2014 the take of the top ten movies ranged from 24 to just under 30 percent, with the average for the five-year period 27 percent.
In 2015–2019 the figure, never lower than 31.7 percent (in 2017), averaged 34 percent, dragged up by how in 2019 it ran 38.5 percent.
Of course, the two years after that (2020, 2021) were so chaotic that it was hard to get much sense out of the numbers, but in that year of comparative recovery, 2022, the proportion was higher still, the top ten movies accounting for 52 percent of the total — more than twice as much as in the decade of the ’00s ($3.85 billion of the $7.37 billion taken in).
And in 2023 so far the top ten have accounted for an even higher 59 percent of the total box office gross ($2.68 billion of the $4.51 billion collected at last count).
The result is that it seems indisputable that there was a trend toward a more top-heavy box office clearly underway over the twenty-first century’s second decade, and especially after 2015, with the pandemic seeming to give it another boost — as, perhaps, it got people out of the habit of going to the theater for anything but the most “must-see” release. Moreover, there seems little sign of the trend reversing, or even slowing, any time soon.