There is a negative incentive in mining too big blocks, as they propagate longer thus giving a higher chance of getting orphaned.
You can try to lift the block size limit in the protocol, but even if the miners had allowed you to do it, they would still be limiting this very size, because of personal incentives - and that's all a developer needs to know about blocksize economics.
That's because the system award makes up most of their incomings, the situation will be different when the tx fee go dominant.
So it makes sense to enlarge the block size before that happens.