The rule change was fully known about in advance, it didn't suprise anyone. And you could contend that the work is now worth more. For a long time mining was economically unrewarding, miners created a blockchain and provided it with power at their own cost and without any guarantee of success or return. Those who joined later were joining when their work would be immediately rewarded with profit because it became economically feasible to mine. These late arrivers actually pushed out a lot of the early miners by using more powerful and efficient equipment. So they may have taken more of a capital risk but less of a risk in terms of knowing a return was possible and would repay their investment.