I'd be shocked if it wasn't a shotgun strategy learned during RLHF or RLVR post-training.

A short response that's wrong is going to be punished, whereas a long answer that contains the correct information, and then a whole bunch of other stuff surrounding that info, is more likely to be rewarded. Even if you discount the reward by answer length, when there's ambiguity involved it's still going to be a better strategy on average to hedge by saying too much vs risking saying too little.