Why is god so biased?

I wonder on what criteria does god decides what we deserve. My parents have always told me that God is watching and you really need to be nice for God to give you what you deserve. Thankfully, good has been kind to me and I have pretty much everything that I can ask for, but there are few good people that I know personally and are not happy with what they have.

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I have know this amazing couple ever since I can remember. They are the nicest people I have ever met and very helpful. God has been kind to them in every way except in gifting them the parental pressure. They have wealth, health and everything they can ask for, but no kids.

Doctors also couldn't help them after several attempts of IVF failed. The wife stays depressed and so does the husband, but he has to maintain a strong face to support the wife who is always taunted by the society for not being able to bear children.

The couple have now accepted that they cannot be parents of a biological child and are considering adoption. I am sure that they would make for good parents.

But I fail to get God's selection criteria for the job of parents. There are hundreds of couple's who do not want children and still get to have kids, while the ones who want desperately doesn't get even one. Parents mistreat their girls because they want boys, but here they would be fine even if they had a girl.

I wish god could explain me why is he so biased.