The idea behind YEC is that God created a world which is visibly, quantifiably, and measurably 6000 years old. According to this, scientists, in their hubris, failed to see what was right in front of them, and were led astray. It’s imperative that the earth NOT appear to be older than 6000 years, because if God put forth evidence that it was that old, then he did so for a reason, and we should treat it as being that old.