It's not like an arbitrary imposition, that's the data it was trained on and it's expensive to train. I hope they find a way to continually train in new information too but it's not like they can just remove the cutoff date.
Not disagreeing, but a fascinating thing they did (as a one-off fine-tune?) was teach ChatGPT about the openai python client library, including the features that were added after the cutoff date.