I'd say it's an energy quanta problem. You can also think of it as a molecular resonance problem and thermal equilibrium problem on the microwave side. By definition, to break a bond you need ionizing radiation. That's photon energy question (E=hf), and microwave frequencies are just far too low. On the other hand, from an electromagnetic perspective, while a water molecule is still tiny compared to a wavelength, it is a polar molecule and does happen to couple well enough to resonate and convert some of the electromagnetic energy to heat. However, the water evaporates and gives up that heat long before the temperature could ever get high enough to dissociate atomic bonds in the water molecule. Likewise, the coupling of the microwave directly to the electron(s) making the bonds is so low they aren't going to see much perturbation at the subatomic level. As far as they're concerned the applied field is quasi-static. The net change to an electron "orbit" is zero.

Thank you so much for you Dr. Michael .

I hope for you a nice day

your sincerely

Qusay Kh. Al_Dulamey