I suppose there could be any number of reasons for the things you just mentioned.
Here are just three that I’ve run across:
My ancestor gave up a child for adoption (prior to her eventual marriage to my ancestor). This baby’s descendant and I found each other though a DNA match, subsequent research, and her brief family information. We both were thrilled to find each other. However, a couple of my distant relatives want to keep this “secret” from their relatives, which I highly respect.
While researching for someone (“John”), I found a despicable, presumed crime for which his ancestor was accused. The ancestor was jailed, eventually the verdict was reversed, and he was released from jail. I continue to research for John and periodically wonder if his ancestor was falsely accused, or did he commit the crime and shouldn’t have been released.
While researching for an elderly friend, I found out his ancestors were from Greece (and another country; I now don’t remember which one). He was devastated as he was always told by his family that their ancestors were German. He never accepted my findings; to this day I wish I had made clear that findings can be upsetting.
So, your cousins could have their own stories, or it could be something as simple as they just aren’t interested in genealogy.
Added: do the matches have any online photographs of their ancestors? If so, do you see any resemblances.