Not everything is black and white, especially in Gotham
It starts with a picture of a boy in Gotham, apparently called Robin and a vigilante/hero.Followed by an uproar, both in the news and within the League.But the information on Batman, and Gotham in general, that the League had was sparse at best.And not everything is black and white, especially in GothamSo they might just end up with more questions than answers and Gotham doesn't take kindly on being intruded upon.
(or alternatively: How the League found out that describing Gotham and its protector(s) with 'The city with the highest crime rate, protected by the vigilante Batman' doesn't even cover one-fifth of the truth.)