For such a large amount, the $ 5 fee does not mean anything. It's still very cheap and affordable. Maybe if the price of bitcoin is expensive and reaches $ 100,000 it is likely that the fee will increase.
Transaction fee is sometimes fixed value that any amount you process so better to transfer big amount for it to be worthwhile. It is just the volume that high but the value is cheap, transaction fee could increase when the price of bitcoin also increase.