Seems to go a long way towards explaining it.
https://news.mit.edu/2023/mit-wins-putnam-math-competition-0223 The MIT math dynasty continues to break records for its performance in the annual William Lowell Putnam Mathematical Competition. For the third year in a row, MIT students corralled all five of the top Putnam Fellow spots, and for the fourth time in as many years, won the Elizabeth Lowell Putnam Prize for the top-scoring woman. In total, a striking 70 out of this year’s top 100 test-takers were MIT students, including 21 of the top 25.
In its 83rd year, the Putnam Competition is the premier mathematical competition for undergraduate students in the United States and Canada and is administered by the Mathematical Association of America (MAA). The intense six-hour exam, which features 12 proof-based math problems, was taken by 3,415 students from 456 institutions on Dec. 3, 2022.
…About half of the top scorers are alumni of the MIT Math PRIMES (Program for Research in Mathematics, Engineering and Science) high school outreach program. This list includes Liu, Robitaille, and Zhu, five of the next top 11, and three out of the next nine winners, along with many of the students receiving honorable mentions.
