Um... Because some LotR names are used as real given names. Also, the names are derived from a legitimate (albeit invented) language, and have real etymological meanings.
Tolkien was a linguist, and he invented Sindarin, Quenya, etc. according to pre-existing laws that "real" languages follow. They're in every way a "real" language, aside from the fact that they were artificially invented in the 20th century by one person.
Proud adopter of 15 PPs. See my profile for their names.