I do not understand why we have to pay for 4 cent per transaction tough, isn't that too much?
Around the year 2140 the block reward is gone. The years before that, it's like 4 satoshi only.
The design includes for more and more transactions, hence and increasing miners fee, to replace the block reward. Currently the miners fee is around 1% of what the miners get, in the future it will be a larger percentage.
Who decides the 0.0001 should be the optimal miners fee?
It's an open market: miners are free to pick the transactions with high fees first.