I’ve rarely had a candidate elect not to give me that information, as they understand it is to help them in the end. In very rare instances, I felt a grand sense of reluctance and in those cases I did the best to explain why it would limit my ability to represent them. At the end of the day, it is your job search and you should feel as comfortable as possible in what can already prove to be a frustrating, irrational, unfair, process.
Hiring managers are bombarded with phone calls all day long. Not just from recruiters, but every possible sales call, vendor and service provider you can think of. It is up to the individual calling to quickly showcase skills, add value and build credibility. If I do not know exact data points on my candidates, someone I’ve met face to face with and say I am representing, that is embarrassing. Instead, with the knowledge we can be confident, fact-based, logical solution providers for candidates and clients alike, and come from a position of strength.
Lastly, if the way that situation was handled was to tell you “you’re being difficult” or I need that to “play ball” then I’d say the recruiter has some work to do. It is our job as recruiters to be the best communicator in the hiring process. There is a necessity to articulate our thoughts, and reasoning, to candidates and clients alike on behalf of another human being.
General rule with recruiters: If the recruiter cannot provide you with logic-based reasons on why they need a piece of information, it is probably not in your best interest to disclose it.