Why do parents create high expectations on their children?

In so many places there is still unfairness going on over boy and girl. Like some places say so much bad things if a girl is born but extremely happy proud and content if a boy is born. I just really dislike this fact. I don't think there should be any differences. But as kids grow older and reach a certain age mostly in their 20s is when parents all of sudden get this life responsibility and stress about marriage. Either they stress the kids so badly that they will just pressure them to settle or others are chill and let them do their thing whether it's finishing job and having proper job then think about marriage. But parents also interfere in their children relationships with their partner. They will be the one reminding you if they are good enough or not. It's like why do they judge and compare based on education, fairness of skin complications, manners, financial/social status.