It goes like this. The writers of old family history books often invented connections. Immigrants with the same surname wre routinely made to be brothers, or father and son, when there was no evidence to connect them at all.
If they found a rich person with the same name in England, that was the immigrant. Loads of immigrants were once placed as Lords and Ladies, who weren't. Failing that, they looked for a baptism in the same name, and that was the immigrant, although there could be many baptisms in the same name in the same year. Failing that, they found a family with the same surname and said the immigrant "undoubtedly" came from that family, and made some excuse for the baptism being missing.
For maiden names of wives, they just filled in any surname connected with the family, eg as a neighbour or witness.
This junk-genealogy all went into print, but usually small print runs for family circulation only.
But later, the LDS collected copies of all the books for the big library.
The LDS also encouraged members to submit copies of all the birth and marriage records they found in their research. That was fine, so long as the members stuck to the records they found in parish registers.
But the members also found the old books in the library and turned the "information" in the books into "birth records" and "marriage records" and submitted them as well. And so the made-up stuff was all mixed in with the records.
LDS members do genealogy for religious reasons. Getting it right isn't important. Some of the members do it very badly. But the LDS treats it all the same. It's not aiming to police genealogical standards, it's aiming to encourage the religious activities of its members. It has, in the past, suppressed data from registers in favour of member contributions, because that's the way it thinks.