Bωockchain

As far as I know the fees are determined by the market, the only thing that decreases is the reward for finding a block. I believe the reasoning about it is to have a limited amount of bitcoins in circulation. If there was no cap on supply then the value of Bitcoin would crumble as essentially in the long term the miners could "print" or "mine" infinitely many of it.

Miners are still though incentivized to keep the security of the network as long as there is demand for transaction. Everytime you put out a transaction on the blockchain you pay a small fee to the miners. The higher the fee the shorter you will have to wait for the bitcoins to be transferred as more miners will be incentivized to put your transaction on the blockchain while mining.

So the reasoning about the whole system is: make at first Bitcoin scarce to encourage mining and as more and more people own the cryptocurrency the more mining will shift from creating Bitcoins out of nowhere to getting money from the transaction fees. At least that's how I understand it.