That's is also why not many people mine bitcoin now, only the people who live in places like China and India, where electricity is dirt cheap can afford to mine. Also why people have higher transaction fees now, to make up for the decreasing amount of block rewards.
That is what I'm thinking. Even in the past there are a alot of bitcoin that is gone. So we can say that the bitcoins in the future will not be having a total number of 21Million but will be close to that total number.
Miners are making a way so they can't waste their money in mining. While the miners are closing to the hardest blocks to mine, they are increasing their fees which I think will be decreasing the time they've mined it all.