Quick correction: the block subsidy is 3.125 BTC per block now, not 6.25. It was cut in half at the April 2024 halving.
Before that it was 6.25, and before that 12.5. Each halving reduces the reward by half. This happens roughly every 4 years and will continue until the last fraction of a Bitcoin is mined around 2140.
You are right that transaction fees become the primary incentive for miners over time. That is a real shift the network will navigate as block rewards shrink toward zero.
