Mining has reached equilibrium. If you invest a certain amount of money in mining gear it will produce about the same amount after some period of time depending how cheap electricity you can find. After that, your gear is outdated and it won't produce anything anymore. Only manufacturers can make profit because they have the fastest chips early and they won't sell those cheaper than they are expecting return.

Block reward is currently 25 BTC so it would cost approximately $10000 to have enough mining devices to solve one block before these devices probably won't solve anything anymore.