When I found my grandfather with most of his children but the wrong wife, I asked how that could happen. I was told that Mormons are required to submit a certain number of genealogies and some people submit almost anything.
I'm not Mormon so I don't know if this is really true.
We are not “required” to submit anything. I have never submitted anything. As I said, the private genealogies on the website are not meant to be taken as “proof” of anything. They are a starting point, to be verified with source documents, when possible. The Church has a large collection of source documents. Those are the most valuable. The private genealogies are more useful in establishing relationships and giving a person a place to start.
Sometimes mistakes are made. Some members are more careful than others when compiling their genealogies. I was taught to try to verify every date, not just accept was Aunt Millie thought was correct. But not everyone does that.
Also, it is easy even for a careful researcher to make a good faith mistake. Then is especially true if there is someone with the same name, in the same location, and the records are sparse.
Anyway, we do the best we can, and genealogists from all over the world appreciate our resources, despite the efforts of some here to denigrate our efforts.