Many selective universities and colleges included only one supplemental essay, and often with fewer words.
"Twice as many essays at twice the length was too much," said one prospective student who chose not to apply.
In contrast to Swarthmore's experience, the University of Pennsylvania dropped a supplemental essay this year, and its applications rose 15 percent.
Swarthmore is concerned enough that it plans to drop one of its supplemental essays before the next admissions cycle.
But can one essay really have that much sway?
"It can make an enormous difference because you're dealing with 17- or 18-year-olds who may not be the best planners in life," said Barmak Nassirian, of the American Association of State Colleges and Universities, a longtime watcher of admissions trends. "It can literally come down to the last three hours before deadline. One essay may not sound like a lot, but it is."
Boston College last year added an essay to attract more students serious about attending; its applicant pool fell 26 percent.
Kenyon College in Ohio this spring dropped three supplemental essays to de-emphasize its branding as a writing school and attract more underrepresented students, including those who would be the first in their family to go to college. Applications rose 63 percent.
"Surely, the supplement was the biggest part of it, but something else was going on, too," said Jennifer Delahunty, dean of admissions and financial aid at Kenyon. She referred to promotional videos for the school created by celebrated author John Green, an alumnus, as another possible factor.
Other selective colleges in the Philadelphia region reported smaller variations in applications this spring, Villanova a 5 percent increase and Haverford a 2.5 percent dip. Both require one supplemental essay.
At Swarthmore, the smaller applicant pool had virtually no effect on the quality of the class, Bock said. SAT scores, GPAs, and other measures of incoming freshmen remained much the same as last year, he said.
"We remain outrageously selective," Bock said.
The college accepted 17 percent of its 5,540 applicants this spring, compared with 14 percent of 6,614 applicants in 2013.
Nonetheless, the numbers reflect a drop in selectivity, long seen as a marker of prestige.
Swarthmore will move to one supplemental essay next year, Bock said, and cap it at 250 words - half this year's maximum.
"We're going to try to remove some of the perceived barriers to applying," Bock said. "We want to be in line with our peers and not an outlier. Will that generate more applications? I don't know. Time will tell."
Bock said the essay was only one factor. Swarthmore and other colleges also were concerned about the impact of glitches in the introduction of changes to the Common Application.
Also, the number of high school graduates has declined, most precipitously in the Northeast. And cost - Swarthmore charged $57,850 in tuition, fees, and room and board last year - is a factor, along with questions from some corners about the worth of a liberal arts education, Bock said.
International applicants and applicants from the western United States fell off this year - both have traditionally been growth markets for Swarthmore.
Another possible reason, not cited by Bock, is that Swarthmore faced intense public scrutiny over the last year and a half over its handling of sexual assaults. Students filed federal complaints against the school, and some students wonder if the publicity affected applications.
Of the overall decline, Bock said: "We may never really know why."
Gains at Penn
At the University of Pennsylvania, Eric Furda, dean of admissions, believes the reduction in essays from two to one was not the major reason for the jump in applications from 31,282 to 35,866.
"You don't have a 15 percent increase in any year because of any one thing. It's not that simple," he said.
He cited Penn's growing international presence as more professors offer free Massive Open Online Courses, or MOOCS.
"That puts Penn at a much higher level of visibility," he said.
And, he said, Penn granted more than 7,000 application fee waivers, up from 4,000 in 2013 - making Penn more accessible to low-income families.
Penn accepted 10 percent of its applicants, down from 12 percent in 2013. It got more selective.