One wants to encourage relatives who have taken a new interest in their family history. One way that many people come to genealogical research now is through DNA testing. The companies that market autosomal tests lead many to conclude that the test is all you need and that the rest is automatic.
Because after all those trees tied to DNA tests are correct. Autosomal DNA tests confirm relationships, but the more distant those relationships are beyond parent/child and sibling relationships, the more potential that the relationship isn’t exactly what the site predicts. Most sites indicate that the predictions are predictions, but that doesn’t stop people from believing that they are 100% correct. The “match” confirms that two test submitters are related, but other, traditional sources, will have to be used to hopefully determine the exact relationship.
And of course those other sources will tell you all sorts of other interesting things about your relatives and their lives.
DNA only helps you figure out who reproduced with whom. There’s more to your ancestor than who they reproduced with.