The real question is why miners aren't mining these transactions to get to the limit. Why are they issuing empty blocks, why don't they even care to change the 750kb parameter to 1mb etc etc. The obvious answer is because the fee incentives are too low, so why should they?
The obvious answer is because the lionshare of their income still comes from the block subsidy. That subsidy has to drop first. Which will happen in due time. Only then empty blocks will not be mined anymore.
The empty blocks is an entirely separate issue also. I believe there have been *some* empty blocks mined when transactions could have been included but the vast majority are mined because the miners are mining before they know which pending transactions are valid (and hence include none).