Because "stakeholder-voted" is not technically or politically feasible. After all, what is included in a block is up to miners. Also, I think in the long term what's good for miners is good for the network, and good for anyone with Bitcoins.

When the hard limit starts to constrain Bitcoin's usefulness, this will tend to cause a decrease in Bitcoin's value, and thus, a decrease in miners' real profit. So, eventually, miners are going to want to increase the limit.