As the block reward goes down miners will make more from transaction fees. And BTC is divisible down to 8 decimal places so effectively there are much more than 21 million units available.
So in other words, the fees we see today are CHEAP compared to what we can anticipate in the future.
That's the problem with proof of work: if it takes $50 worth of energy to process a transaction, somewhere, somebody's going to have to pay for it. There's no getting around that economic reality.