My bitcoin reward keeps decreasing!?

[Domino]

Since that's how Bitcoin and the miner community is, it's a lot more profitable if you moved your hashing power to
a different cryptocurrency (SHA 256 that is) since you can get a lot more of the coins and just exchange it for
a better value than you are getting with mining bitcoin.

Or more easily, you can point your hashrate to a profit-switching pool, and the pool will keep tracking the profitability and choose the best coin for you automatically.