Is it possible that one reason people delay checking is because of the (unfounded) stigma associated with being a carrier of one of the genetic diseases? If someone checks with DY before the first date, rather than later in the process, then it’s more likely (just because more matches are being suggested) that at some point a suggested match will be rejected by DY, revealing that both individuals are carriers for one or more fatal diseases. If they wait to check, then the match may well be rejected for other reasons. If both are later redd to and marry non-carriers, their carrier status might never be known.
I’m not saying that this makes sense, but I think that there is a stigma associated with being a carrier exists (even though there are no health risks associated with it as with, say, sickle cell). In fact if I understand correctly, these taboos are the reason behind some of DY’s rules.