The males secret the enzyme that dissolves their jaws though, I believe, not the females.
Stepwise, I think it's easy to visualize how this could have happened, especially when you remember sexual dimorphism is a thing. Males that continued expressing angiogenic factors were able to subsist off more than just bits bitten off from the females. Males that chose to never release never lost their mates. The 'males melting themselves to the female', in my opinion, is likely an energy saving mechanism to alleviate the need to cling to the female using energy from jaw muscles.
-I know this: if life is illusion, then I am no less an illusion, and being thus, the illusion is real to me. I live, I burn with life, I love, I slay, and am content.
-We can't go back. But I suppose we can go wherever we please.