Dorna have decided that they need the spec ECU more than they need Honda.
Why? I'm not saying you're wrong, but I can't understand the logic. I've tried to imagine a scenario in which Dorna benefits from a spec-ECU, despite HRC's probable withdrawal, but the scenarios seem relatively far fetched.
1. Dorna has a handful of manufacturers who are eager to join MotoGP is a spec ECU is implemented. Sounds like fiction to me.
2. The cost of regulating an electronics war is more than the sum cost of testing and implementing a spec-ecu AND the value of the damage done to MotoGP's brand.