After a block is mined, the miner collects new transactions from the mempool for the new block. During this collection period, it makes economically sense for the miner to mine empty blocks.

One could say, that this is a waste of resources, or that it is unfair.

But since Bitcoin is permissionless and it is allowed by the protocol to mine empty blocks, everyone is free to do so. The disincentive for mining empty blocks is the missing out on transaction fees collected by the miner of a block