Everyone that's assuming Rey is related to Luke is assuming thatSpoiler:she was hidden on Jakku after the massacre at the Jedi Temple. But wouldn't it make just as much sense to assume she could have been hidden since Jedi are not supposed to be in love or have children. Yes, Anakin does it anyway and Luke has no council to answer to but it would still make sense that he'd want his padawans to focus on training and not falling in love and he'd be setting a bad example to have his own child running around the Temple.
anakin was born without a father, immaculate conception
Perhaps Rey is Luke Immaculate conception