... It's rare?
It's simply an empty block... It isn't super common, but it does occur relatively often.
How possible happend with that? Then how about reward miners?
Miner still gets the full 12.5 BTC as the block reward. They just don't get fees. But the actual block reward is the main component of the total reward anyway... a lot of blocks are in the 13 BTC reward range even with fees... so miner is only "missing" ~0.5 BTC for mining an empty block in that instance.