I think that the rules someone posted here said "no relatives." It was from a different state, though, so that may not be the reason.
For JB and J'chelle, marriage is a big carrot. Once you get married you become an adult with some agency: you can have sex, spend time alone, go to the bathroom by yourself, etc. If getting married puts you in line to host Josh, that's a huge, gigantic stick dwarfing that little carrot.