There could be a couple of reasons your crumble isn’t crispy. You want to make sure your butter is cold when you first cut it in. Be careful not to overmix, and to bake until your topping is golden brown! Sometimes a crumble topping is actually too thick (I know, le gasp), and it could be that you didn’t spread it evenly enough over the fruit so it becomes soggy. It’s all about balance!