I agree they should have tried to find more ways to keep the old behavior. MV3 rollout has already been delayed for a long time, and now users merely get a message. I'm not sure that the community (mostly Google contributors) won't give in or try to find a way to keep MV2. However, what was done with MV2 can now be done with MV3 with native messaging or other network tools... I think the concern is that allowing an exception makes it much easier for a malicious extension or software to get users to agree not realizing what they're agreeing to. Furthermore, the declarative approach is actually preferable by many. You get most of the same features without exposing all your traffic to an extension.