I appreciate the answers, but the "increases security" reason seems like nonsense to me. The purpose of the block is not to provide security, it is to record transactions. Security is inherent in the way the network was designed.
No, any node can arbitrarily record any transactions it wants without miners.
Mining's primary purpose is to provide security for them.
"Empty" blocks are not really empty either: they still include every transaction mined by the prior blocks.
And since 1 block is not sufficient to confirm a transaction, it's really the block 5 down the chain which is beneficial to the transactions in the block mined anyway.