I'd like to response with another question. Imagine that you have international project with 20 countries involved, but 90% of your income is generated by USA customers. Which format you will choose? USA or Canadian? Another use case, imagine, that initially all your customers where from USA and only in two years after launching your product, you got those customers in other countries. What as usually customers ask: change format of dates or some other feature. From my experience issue with dates formatting was in backlog, but as usually it is not in high priority.