Transaction fees, even when they're really expensive like they currently are on the Bitcoin chain, are still minimal in comparison to the block reward of 12.5 Bitcoins (or about $51,250 at current prices) per block found.

Here's a link to a recent full block found on the Bitcoin chain, total transaction fees were 0.43 BTC (or about $1,750).

Recent Full Block on Bitcoin Chain - https://blockchain.info/block/00000000000000000112ebb0462fe5...