Mining 0 fee transactions If a miner is payed per block found, why not scrape the bottom of the barrel and full up blocks with 0 fee transactions? You would still be getting coins for blocks found just not the fees. The bonus would be no competition on finding blocks. Win/win for everyone...
Because fees + 12.5 BTC > 0 + 12.5 BTC. It is a lose for the miner because they could have picked transactions that would have paid them more.