Because the incentive has been changed from the true best output always, to a mix of "close to the best but not always" output.
For the (majority) of us using Claude models for computing as a tool, obviously we're not going to be thrilled that our new tool will perform worse going forward.
For the (majority) of us using Claude models for computing as a tool, obviously we're not going to be thrilled that our new tool will perform worse going forward.