But for some reason, Antpool has the highest number of empty blocks, while Foundry USA has none in the last one year. What is Foundry USA doing that Antpool is not doing?
It is not as if Antpool 'purposely' wants to to mine empty blocks, surely they would prefer to earn tx fees that would have been attached to tx's in the mined block, but if it is empty all they earn is just the coinbase reward. Now that tx fees are kind of high, no mining pool would be happy mining an empty block.
Mining pools are competing with one another to mine blocks and earn the reward, so speed in addition to their computational power matters a lot, as a result of this, miners could start working on an empty block without any tx in it, only to update the block after a few seconds, but then with tx's in it. However within that few seconds of working on that empty block, the mining pool can successfully mine that block and add it to the blockchain, without any tx's in it.