From the technical standpoint of "The Big 10", actually they did...
Any pastor I have ever talked to has clearly stated that nookie outside of marriage (or even the desire to have do it with some one you are not married to, see Matthew 5:28) is a no-no. Even if you "fix" it later by marrying.
I must add, given my own record in that area, that I would certainly not be in the line to cast stones in this case and applaud the couple for not adding murder to the list of things they need to ask God's mercy to cover.
The marriage ceremony wasn’t even invented until the 3rd or 4th century AD.
From the standpoint of strict biblical interpretation, copulation itself is the act of “marriage”. The marriage ceremony just formalizes this union.
That is, you marry the first person with whom you have sex. All sexual relations with another person are adultery.
Premarital nookie, even when you go ahead and marry your sweetie, still cheapens the ultimate union. Of course, the common thing today is not to marry, but to go on to somebody else, and then another and another ad nauseam until most couples have a string of exes on both sides. It's hard enough to love when you have only loved one; what is it like when that flawed individual must compete for your attention with a Louvre of sexual memories (all made glowingly positive by the passage of time)?
I remember in the Sixties when the slick mags were promoting the sexual revolution by talking about "victimless crimes". Apparently, what consenting adults did behind closed doors harmed no one, therefore no one had the right to complain of it. What do we say now that we know what the harm is?
The answer seems to be, we're not allowed to talk about it. That's "imposing" values.