Put another way, the miners will sell that 12.5 BTC on the market. Selling on the market puts a downward pressure on the price.
Another way still: If the market cap for Bitcoin remained constant, then it's obvious to see that for every block reward generated, the price per bitcoin goes down.
I don't think it's unreasonable to think that that means we're paying miners $16.5k USD per block, which would be about $9.22/transaction. Plus transaction fees. It's probably just hard to see that because the market cap for Bitcoin keeps increasing faster than Bitcoin's natural inflation. Basically, investors in Bitcoin are paying the transaction cost right now.