Pools combine power, but all focus on a block? How do they all earn?
Generally (in centralized mining pools), the block everyone is working on mining in the pool, is a block which pays the pool owner. When a valid block is found, the pool owner receives the reward and distributes it to the members in the pool. So every block found, each user receives a little bit of the total reward, generating a more steady income stream for the members who own their own would have very little chance of ever finding a block and getting paid the entire reward.

There is no way for a member of the pool to change who the block pays, without being excluded from the share of the rest of the pool, if they tried to change it to make it pay themselves they would just be solo-mining