Blocks are full, transactions are backing up, fees are rising such that it would make a significant difference to the block reward if you could include twice as many transactions.
I mean.....
Do you even economics?
I think your confusion is trying to apply economics to something that is grade school math,
100 transactions with a 0.1 fee = 10BTC reward
200 transactions with a 0.1 fee = 20BTC reward
heres the complicated bit, pay attention
20 > 10
Jesus christ you are stupid.
So subsidizing transactions by increasing supply will keep average transaction fee constant. Got that...
It will keep average transaction fees as competitive as possible.