Apropos:  Bitcoin mining is NP-hard (or rather, transaction selection is).  The upshot is that it doesn’t get solved optimally, at least from a theoretical perspective.  In practice, “good enough” is good enough:  Fill your knapsack mostly full of mostly the best stuff, and start hashing.  The race is on, and time is critical!

There are all sorts of prickly points around the subtle art of selecting transactions for inclusion in a block.  When making changes to Bitcoin, careful engineering work can be required to at least not make it harder.


Unless they want to attack Bitcoin by deliberately mining empty blocks.  (Here, “empty” means with only the coinbase transaction.)  There is suspicion that this has happened.  Empty blocks are also sometimes produced for other reasons as DannyHamilton explained.