When I first asked about landing on grass, I couldn't find anyone at the school who'd done so. I went ahead and did it anyway. When I asked about flying taildraggers, ditto. This included instructors.
They're not all like that, but let's face it, someone who gets a PPL and an FI rating as a route to the airlines isn't going to fly a tailwheel aircraft into a short grass strip (or even a longer one) or necessarily empathise with someone else who wants to, are they?
The basic trouble is, students and new PPLs think every instructor is a demi-god and the fount of all knowledge on all things aviation. As a new(ish) rotary FI, I'll tell you, we're not!! An FI course teaches us a bit more about flying, and how to teach others to do it to a basic level, in the machines we're likely to be teaching on. That's all. We are not experts on other sorts of flying, other types of flying machine (which is why I show my lack of knowledge of f/w flying with monotonous regularity), aeronautical engineering, or the finer points of air law in obscure third world countries. We know how to teach you to fly and get through your ground exams, that's all.
However, I hope that if someone asked me about flying self-build helicopters in the Scottish Highlands, I'd at least give them an idea of where to go to find out about it. Putting people off, unless its something obviously dangerous, is not on, IMHO.