Isn't it obvious? Someone's "temporary hack" stopped working, and even though it's not been important enough to refactor for the past 100 years it's important enough to drop everything right now to fix when it breaks.
PL research and reverse engineering or just fixing compatibility. Say you want a program from 3.6 era but the 107 year old interpreter doesn't quite suit you and the newest one broke something, and you bisect interpreter versions to find 3.11 to 3.12 broke it.
Multiplanetary species that has merged with AI thanks to neuralink-esque tech discovers a bug in the brains of 5% of the population. Turns out the bug is due to Python 3.12 which was used to write the natural language understanding (NLU) engine of the brain chips.