Well goody for you. Evasive much?
Yes... And no. I think you are more than capable of thinking of reasons a man, or woman would prefer his/her significant other be chaste before marriage. You were being evasive-- and I find that very childish/dishonest. For that reason, I was willing to return that evasiveness. But, I will humble myself and answer your question.
I have a bar of soap in the shower. I used that bar of soap yesterday morning. Today, I decide to give that bar of soap as a gift. I clean the bar of soap from all signs of my previous use. I then wrap the bar up, and give it to you. You unwrap the bar of soap, and use it the following morning. You then decide that you want to give the bar of soap as a gift. You do not clean the bar of soap. Instead, you leave hair and dirt visible on the soap. You wrap it up, and give it as a gift to your friend. Your friend unwraps the bar of soap, and sees that it has been used. Your friend is not disturbed; your friend is equally grateful to have a bar of soap, and uses it longer than everyone before him. Eventually, your friend also decides that the soap is worthy of being given as a gift.
Who valued the soap more than the others? Apparently no one. They all valued the soap equally, utilizing it in the same manner, and then gifting it. Did the soap work harder, or better, for any of the people who utilized it? Apparently not.
Your friend wraps the soap up, and gives it as a gift to another friend. That friend unwraps the soap and accepts the gift. That friend also has another bar of soap, that is unused. He uses both bars of soap. That friend then decides to give a bar of soap for a gift. That friend reasons, "Both are equally useful.. But I am the only one who has used this bar. I know this bar even more than the other, because I have not known the other's origin or travels. If anything, I can remain loyal to the bar I have known since its origin, and it will always be known to me. No one will be able to say they received more or less from my bar, because I will receive it all. This bar will also know more of me, than it would if it were passed along." So that friend wraps up the other bar and gives it as a gift. This time, when the bar is unwrapped by its recipient, the recipient is perplexed. It has obviously been reused many times. The last recipient says about the soap; "Is there something wrong with this soap, that not one person decided to keep it for themselves? Why should I keep it at all?" The gifter then says, "Nope; it was a perfectly useful gift." The recipient then accepts the gift, and uses it gratefully. After a while, the recipient receives a rash, which the doctor determines resulted from the uncleanliness of the soap. The doctor suggests that the recipient knows the history of any other soap before using, to avoid similar circumstances from recurring. The recipient then decides it is easier to use unused soap, from then on, than to inquire about all the other recipients of a particular bar of soap.
Now..
Imagine living thousands of years ago, when people were aware of sexually transmitted diseases, but unsure of their exact transmission methods, etc-- and unable to call a doctor and ask who, where and why.
Imagine being a man who marries a woman who doesn't know she's pregnant. You end up thinking you have a child, when in fact you're raising someone else's.
Imagine that tomorrow your marriage partner, who has an extensive sexual history, one day decides that you aren't up to par with their previous partners. Your partner decides that instead of having mediocre sexual relations with you all the time, they'll introduce their previous sexual partner, or divorce you. Consider that your partner may not wish to hurt your feelings, and instead of being forthcoming, cheats whenever possible.
Imagine having children by three different men. All three like to travel. All three like to see their children on a regular basis. Your current man doesn't like the other three at all. Imagine the complications, especially thousands or even hundreds of years ago.