Because they didn't have your name back then, they do now, and they've connected the dots. If Hitsugaya wants to press the issue, you're getting arrested and dragged to Seireitei, then whats going to happen to your kids? Who's gonna explain that Daddy fucked up and is in jail for pranking his successor in his old job, which happened to be the same people who want him dead?

Because its too obvious, too many people who could potentially identify you and give your name. And you don't want that, don't you? Or you didn't.