the avg transaction fee for Bitcoin Cash BCH is 0.3 USD .30 cents (is thao correct?)
I don't know. I don't pay much attention to what's happening with BCH.
if so why and how could there be such a difference?
More people want to use Bitcoin, so they are willing to pay more for the limited space available.
I know more miners =lower fees but that much lower?
Not true.
more transactions = higher fees. Less transactions = lower fees.
The number of miners doesn't directly effect the transaction cost.
The relationship is mostly the other way around...
If there are more fees (and therefore more money to earn from fees) then it will attract more miners.