I have found a very common frustration among family historians. A researcher finds a new cousin, or another researcher with common research interests, then that new contact becomes incommunicado. POOF! Disappears into thin air! In many of the stories I hear, this new contact seemed very enthusiastic about genealogy or about finding a new family connection. Usually, this person received far more information than he or she shared. Many times, this person hints about or claims to possess valuable family information. So, why the disappearing act?
I think, although the stories are the same, the reasons people hide are too diverse to generalize. Some people get excited about meeting a new relative, then think twice about getting involved with more family members. Others want the information, but they are possessive about their own records and photos, and simply don't want to share. Some envision themselves as THE family historian, and don't like sharing the title. And, some are just plain cantankerous!
The disappearances I don't quite understand myself are the fellow researchers who don't respond or who disappear after getting the help they need. I am hearing more and more complaints from people who have had their DNA tested, have contacted their matches, and don't hear back. These matches are people who also have had their DNA tested for genealogical purposes and who signed a consent form to be contacted. They also paid a hefty sum to get their DNA tested for genealogical purposes. Why don't they follow through?
I see this lack of responsiveness as a real and growing problem in genealogy. I know quite a few family historians who are now much more possessive about their work product and records because they were "burned" too many times by people who took their work and disappeared. Access to records and communication with relatives and fellow researchers are the key tools relied upon by family historians. Sharing and helping each other is crucial to us.
What to do?
Short of pestering, burglary (just kidding!!), and becoming more possessive ourselves, there is little we can do to force someone to communicate. In the law, there is an old legal principle that it is easier to restrain a person from doing an act than it is to force a person to act. Some people respond to repeated requests, others are put off by what they perceive as pestering and shut up tighter than a clam shell.
The most effective methods reported by other researchers seems to be bribery and third-party involvement. I know some researchers who will not share all of their work product with a new contact. They use the promise of "more information to come" as an encouragement for the other person to share. I have also heard successful stories of other relatives or friends interceding with the recalcitrant person to obtain the needed information.
But I do find it hard, myself, not to feel a bit "burned" when a contact drops out of sight, especially after getting my information and sharing none in return.