The medium at the Spiritualist service I attended last Sunday talked about this very subject in her address.
The way she explained the often nebulous contact between the spirit world and our physical world was that, if spirit manifested itself completely and on command so there could be absolutely no doubt as to its existence and wisdom, then we would never bother developing for ourselves. We would just ask for, and get, any information we required without having to think, experience and grow ourselves. The challenge of this life would be negated if spirit always told us unambiguously what was "in the next room".
I know a committed sceptic would say this explanation was a cop out, but if you try and look at it objectively, it seems reasonable enough to me. And besides, the spirit world isn't obliged to make contact at all. For all we know they might be occupied doing much more important and wide-ranging development of their own, without being at our beck and call down here asking them stupid things like what card someone is holding up next door! lol
Love and Light,
Jeremy