Pregnancy testing and getting BFP

It confuses me why some women can test and get a BFP at 8 or 9dpo while others don't see it until 12, 13, or 14+ dpo. Do you all think this is just because maybe the egg doesn't implant at the same time for everyone? Or do you think some people are actually farther along than they think they are or had their ovulation date wrong? Just don't understand why it takes some longer to see BFP than others. Any insight?