Please rank in the order of importance. Here’re some suggested factors (feel free to add your own):
- Uncertainty in admission (low admit rates)
- Ease of application due to Common App, etc.
- Effective marketing by colleges
- More colleges offering fee waivers, dropping or reducing standardized testing requirements and/or supplemental essays, etc.
- Chance at top ranked colleges even if the probabilities are extremely low
- Need to shop around for better financial aid
- More applicants this year (year 2000/Chinese Year of Dragon effect)
- More international applicants
On a time scale measured in decades, the population of high school graduates has increased faster than the number of spaces in the most desired colleges. Yes, some colleges have been built, but most new colleges start at the bottom of the desirability / prestige scale.
Also, there is a greater tendency for high school kids and parents to see college as a necessary step toward a good career, so that increases the interest in college beyond just what population increases have caused.
Regarding extra kids born in “special years” (whether the usual calendar years of Chinese zodiac calendar years), note that such years do not line up with the cutoff birthdays for kindergarten enrollment, so the extra applicants will be spread across two application years.
I have no data except for anecdotal experience. Personally, the driving factor is the ever decreasing admit rates of colleges across the boards. The more we read about kids being rejected from colleges that appeared safe, the more colleges we are all add to our lists.