Almost all of the comments have someone’s pet theory about the cause of the decline in achievement. The truth is we don’t actually know why there is a decline or how to stop it.
The truth is obvious, you just don't like the solution.
Speaking as a PhD in math, Olympiad problems are very different than ordinary research math problems. Olympiad math problems in particular don't require creating new theory, but rather brilliance and knowing a bunch of standard tricks and how to apply them in insightful ways.
Becoming good at solving Olympiad problems won't really give you much skill in solving creative research problems, but it does give some indication of pure ingenuity as one dimension of mathematical intelligence.
Then, I need to understand and modify the evaluation behavior of a deeply-layered external software stack, including its crazy type-level magic, all before a looming deadline.
Seriously, how is this good for my sanity or career?