The article mentions why this is important but doesn't really explain the details. We don't have an equation of state [1] for neutron stars. Part of the reason

The article mentions why this is important but doesn't really explain the details. We don't have an equation of state [1] for neutron stars. Part of the reason why is that neutron stars are incredibly complex. You have fluid dynamics. Because matter is so dense you likely have neotronium and probably weird states and interactions with quarks. Contrast this with black holes. Black holes can be perfectly described with 3 properties, only 2 of which are really relevant. The two relevant ones are spin and mass. The less relevant one is electric charge. Why is it less relevant? Because if the charge is too high then it can't be a black hole. Because of this we can calculate how large black holes can be, figure out the fastest that they can grow (ie by sucking matter from the accretion disk; there's an uppper bound to that), etc. So we have a rough guess on the range of masses neutron stars can be but we observation is really our only tool here. This is why examples outside of our estimated range are important. [1]: https://en.wikipedia.org/wiki/Equation_of_state https://en.wikipedia.org/wiki/Equation_of_state