So fortunately there shouldn't be a situation where miners are deliberately mining transactionless blocks. Occasionally it happens by pure chance but that's just the random nature of block generation.
Of course I suppose you could argue that a miner might mine transactionless blocks in order to cut down on the block size for faster propagation, but that'd seem pretty counter productive.
Except that it isn't necessarily counterproductive to mine empty blocks to get faster propagation. The propagation time depends on the number of transactions in the block, so a miner could make an estimate of the odds of a block being orphaned due to slow propagation and weigh the potential losses of an orphaned block against the certain losses of not including fee-paying transactions.
With fees still being a very small part of the block reward, the answer may not be obvious.