If the block template contains no txs, and the miners find a block before the template is repopulated with txs from the mempool, they are incentivized to claim the block reward before someone else finds a block.

It’s a race. All that matters is the sats you can claim by broadcasting the next valid block.

The idea is that if a mining pool does this often, the miners will switch to a pool that produces full blocks, as their Payout per share (the lesser difficulty proof that you are mining) be larger.