"You are one of the most money savvy people I've ever met and you're a sixth year. Are you planning to be a financial advisor to witches and wizards after you leave Hogwarts?" Brinley partially joked but wouldn't be surprised if that somehow ended up working into it somehow. But it did beg the question, "So what exactly are you saving all this for? Are you saving to buy a thing . . . or what?"
It was something Brinley wanted to know, primarily because someone who took the effort to not only set up various accounts, but knowing what they're doing and keep track of what's going on with them had to have a purpose for it. Unless Bailey just had a very strong interest in Wall Street.