I'm watching Japanese education videos on YouTube, and there are quite a few students who got into former Imperial Universities but failed Waseda or Keio

‌Not just the Imperial Universities,
but there are also students who failed Waseda or Keio and got into Hitotsubashi (the 3rd ranked university for humanities),
and there are even students who failed Meiji University but got into other schools.
They mentioned that national universities require 5 subjects while private universities require 3, but the admission processes seem incredibly diverse.
Even among private universities, some entrance exams include the Center Test while others do not.
It seems there are also students who failed Waseda or Keio but got into Nagoya University or Osaka University.