The argument to make it grade based two years ago was to do more teams. But the question was never answered: why not just do one year age based teams?
Like another poster wrote, the U-11, U-13 and U-15 did put kids a year older out there, but in that system every kid gets to be the older kid once. With grade based it just created a permanent imbalance between parents who can afford to shelve their kids in private schools for a repeat year versus the families who decided to not do it or could not afford it. That isn't a good way to administer a youth sport.