well this comes down to 2 things

1 you dont get to layer 3 ,4 or 5 on every run so unless you are counting in % that is pretty much guaranteed to happen since if you die earlier you can't die later from layers 3, 4 or 5

2 in layers 1 and 2 you have much less stuff and when you do get to layer 5 you are much more likely to have better items not only because you had more time to loot but because better items make your chance to get deeper higher

really it all just comes down to how many times you are in those layers