Finding the nonce for a block in the blockchain is equivalent to creating a small fraction of a bitcoin.
When a nonce is found for the next block, creating n bitcoin worth of value, the user's ID is updated with the additional credit of n bitcoin on the chain.
After a block is mined, such as block 1000, the focus shifts to finding the nonce for the next block, like block 1001, as future blocks cannot be mined until the previous ones are finalized.
The competition in mining is centered around finding the specific nonce for the next block in the chain, not on searching for any possible bitcoin value, similar to the diminishing availability and increasing difficulty of finding gold.