More to the point:
- Why would God give everything the appearance of being 4.5 billion years old if in fact it wasn’t?
- Why would God give everything the appearance of having used macro-evolution if in fact He hadn’t?
- Conversely, why would God expect us to believe that He hadn’t used macro-evolution to create everything if in fact He had?
Basically, your question boils down to, why did God create everything with the appearance that it has?
Here’s the thing. There is such a thing as objective reality. Facts are facts and not opinions. Many things that God has created bear clear, unambiguous and insistent evidence of specific sequences of events having happened at specific times with specific causes and specific effects. And contrary to what YECs claim, the evidence cannot be interpreted in different ways depending on which “lens” you look at it through. There are strict rules that interpretations must follow (basically, the rules of measurement and mathematics) and it is those rules that tell us in no uncertain terms that some interpretations are legitimate and valid while others are not.
Could God have created everything in an instant? I have no doubt that He could. But why would He have created vast swathes of very detailed and self-consistent evidence for 4.5 billion years of events that had never happened?
I don’t think there’s any reason why we should be upset as Christians at the thought of macroevolution. The main reason why people don’t like it isn’t because they think it’s unbiblical, but because they are proud. They don’t like the thought of being related to the animals, because it makes them less important than they like to think they are. But the Bible itself tells us pretty much the same thing in Ecclesiastes 3:18-21 anyway:
I also said to myself, “As for humans, God tests them so that they may see that they are like the animals. Surely the fate of human beings is like that of the animals; the same fate awaits them both: As one dies, so dies the other. All have the same breath; humans have no advantage over animals. Everything is meaningless. All go to the same place; all come from dust, and to dust all return. Who knows if the human spirit rises upward and if the spirit of the animal goes down into the earth?”