What determines whether the merger is non-radiative in the EM? Why was the collision of two neutron stars radiative? It seems like the universe would be immeas

What determines whether the merger is non-radiative in the EM? Why was the collision of two neutron stars radiative? It seems like the universe would be immeasurably more dangerous than it already is, if all of these events were primarily EM radiative in nature. As a non-physicist, I'm also curious how gravity is simultaneously so much weaker than the other forces, but yet spacetime seems to be able to stably survive these immense releases of energy.