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I have observed many times whenever there is rise in the price it will proportionally increase the fees as well. BTC becomes useless if I want transfer my coffee bill worth $5 or lets say lunch of $50 bucks if I have to pay more than 10-15 USD for single transaction.
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You did really experienced paying 10-15 USD for a single transaction with $5- $50 input? Personally I never experienced that one.
AFAIK, the transaction fee is relative to the traffic on the mempool. The higher the congestion is, the higher the fee will become. I'm not really so sure, but that's what I think the reason behind it.
People are paying higher too become more priority on the mempool. Racing to be accepted first.