A few confounding factors come up right away: one of professors removed final project which increased grades; due to less appealing CS career, you do not get the best students anymore: another professor is not a fan of curving so perhaps he just accidentally gave harder tests; math prep for CS courses happened over the last 15 years not last 2 where LLMs have become ubiquitous; many failed because they were caught using LLMs when not allowed...

So really, two professors' gut feel about what the reasons are and not backed by much.