Simply. 1 Block (currently) = 25BTC. This block doesn't have to be full of transactions to be sent out. Even if it isn't full, it's still worth 25BTC and the amount of miners hacking at the same block does not decrease at any point in time. Miners decreasing = less difficulty. Miners increasing = more difficulty. Difficulty is not affected by number of transactions running through it.
For instance if you go to a newly released altcoin that people don't transact quickly/at all, the blocks keep coming and miners keep mining.
To be honest, it is a stupid question.
