Because some people for a variety of reasons choose to leave no records behind of certain events.
15 September 2014
Not Everyone Has One
Some people simply don't leave certain types of records. I have a relative who died in the last ten years for whom there is no death notice, no obituary, and no estate settlement (despite having children and grandchildren and sufficient personal property). Some people live as husband and wife and never actually "get married," so there is no "marriage record." Others avoid the census taker at one or more times in their lives. Sometimes it is worth contemplating that the record for which you are looking simply does not exist.
Posted by Bubba