I think what the miners are afraid of, is that the power of the bitcoin network, leaves their hands and fall into the hands of second layer operators. At the same time, a higher blockchain size would make it less profitable for small miners, to mine bitcoin. Bitfury recently released an analysis, that predicts that 95% of current miners, would find mining to be unprofitable at blocksize of 8MB. This would further centralize profits and power over the protocol, with the big datacenter miners.