Because mining is every time harder, and hence more expensive, right now is profitable because the btc is rising, but what will happen when btc price is stable and miners won't get any extra reward, only the fee.
If the fee is high then we will end in a worst scenario than current transactions with banks :(
Is there any approximation about this fee? (In btc because we won't know the price in usd)
similar question (but too old, without answer): How much will transaction fees eventually be?
Maybe this could be a good approximation
How many BTC are transferred per day (daily volume)?: 750.000 BTC (source: https://coinmarketcap.com/currencies/bitcoin)
How many BTC are mined (generated as reward) every day?: 1800 BTC (source: https://www.bitcoinblockhalf.com/)
How much is paid in fee every day?: 34 BTC (source: https://blockchain.info/stats)
So right now the fee is 34 / 750.000 = 0.0045%
But if we mined everything, then we need to pay the 1800BTC to miners in fees to compensate so will be (1800+34) / 750.000 = 0.25%
If this is the case I think is cheaper than current bank transactions fees...
But I'm not sure if this is a valid approximation, fee seems to change a lot (not sure why or even how to read this graph either): https://bitcoinfees.info/