Zaphod - Never really thought about it, I just get these messages from time to time. I suppose it's related to how many matches you have, I started with 16,000 and it''s crept up to 26,000 over the years but I've spoken to Americans who have over 100,000. Some (very small) percentage of them are curious enough to make contact.
It's the two that didn't reply to me that were really strange, one was a 2nd cousin whose grandmother I knew quite well and the other was a self-proclaimed professional genealogist. The latter changed the name of the account, made the tree private, and changed the name on the managing account, all immediately after I contacted them and all very peculiar. My theory is they were charging for their work and didn't want to be seen receiving information from me.
PS. Not sure I would know how to make myself interesting !