All it takes is for one person to make a mistake on a family tree. Then other people who don't know how to verify information copy that mistake onto their tree. (They think research means finding something online, even without a source, and adding that to make their tree as big as possible.) Soon there are many trees with exactly the same wrong information. Usually the only "sources" are the family trees they've found.
Serious researchers won't take the trees seriously without real sources. Just make sure your tree is properly sourced and don't worry about the other trees.