Here is the part most people miss.
Hashrate is a relative number, not an absolute one. Your miner does not earn more BTC simply because its hashrate went up — it earns more BTC when its hashrate grows faster than the rest of the network's hashrate.
And right now, global hashrate climbs roughly 30 to 50% every year, much like a tide that keeps rising under every boat in the harbour.
This is why a miner sitting still slowly earns less over time, while a miner that keeps pace or pulls ahead keeps its share of the pie.