way to minimize personal values of someone. it means nothing TO YOU. keep that in mind. It is neither irrational or unreasonable to expect and based one one's moral values, I don't think you can just write it off as being something that has no benefit just because this is how you view it. Just because physically it may offer no benefit, the spiritual side of things is something you can't easily write off except state your opinion on whether or not it's important.

To answer the OP's question more directly, it's because it's become commonplace in today's world to have sex without the expectation of exclusive relationships, let alone marriage. It's become the norm, for many so the ones that still believe that sex only after marriage is important have become harder to find.

As others have said, change where you seek partners and find groups where people are like minded in this regard, one place being in a religious setting or church.