The reason the date is somewhat later this year is because the Ivy League schools have seen a major jump in applications. For example, last year Harvard received 40,248 applicants, but this year it received over 57,000! That's by far its highest number of applications in a single admissions cycle.
Many Ivy League schools have seen similar increases in application numbers. The reason is hard to know right now, but it's possible that when Ivy League schools dropped their ACT/SAT requirements due to the coronavirus pandemic, that convinced more students to apply who normally wouldn't have.