Re: Why is it so?
My reaction if i was in the parent's position would be a little anger, but open mindedness. If the son/daughter truly like this person, I would not marry them off to someone else and make some other poor guy/girl suffer from being in a marriage of unrequited love. You ask why do people make an issue of it? probably because the son/daughter hid it from the parents for a long time. Why do the kids hide their relationships from their parents? If there is some interest between a guy/girl, parents should be involved right away. None of this dating for a year keeping it hidden from mom and dad, then telling them they want to get married. If the marriage doesn't go through, the kid now has to deal with the emotional baggage. Parents wonder if they guy their daughter chose just wants to take advantage of her or already has, or in the case of a son, they wonder if the girl just wants the their son for his money, compliant personality, etc.
They also may have raised their kid telling them it's wrong to hang out with boys/girls and now they find out their son/daughter has been seeing someone behind their backs. Its easy enough to feel totally betrayed. I know the only thing the daughter/son can see is the person they want to marry, but please look at the parents' perspective, the people who gave all and raised this person. Islamically you have a right to choose your spouse, but you also have an obligation to respect your parents. How do you show respect by just telling them out of the blue that you have made the biggest decision of your life and you didn't think it was important to involve them in the decision making process?
Also, when you say a mature person, do you mean a college-aged person? Because to me, a college aged person is not mature; breaking the news to your parents if you are still below 22 will not be taken well. A mature person would be someone who is not living off mom and dad and have been on their own for a while. In this case, I don't think a parent would be shocked at all, they would probably be relieved. If you still live with mom and dad, you have an obligation to tell them what is going on in your life.