This may well vary from broker to broker, and it may depend on the specific contractual details of the listing agreement. It is possible that this broker's listing agreement is written in a way that they genuinely cannot share that information.
Of course, they might have just decided it is better for their business to not disclose it, even though they can, and this is the easiest way to tell you "I won't tell you."
We might want it, and it might help us make valuation/purchase decisions, but that's not the same as being entitled to it. If (not) having that information is make-or-break, just shop elsewhere.