I cannot see why what exists beyond the event horizon needs to of quasi infinite density, the matereal of a Neutron star has nearly a high enough density to produce an event horizon so why does the contents of a black hole have to be vastly greater

A neutron star doesn't have enough density to produce an event horizon. Assuming it does is due to mistakenly applying a solution to GR which is valid in empty space to the region within the neutron star as well.

An analogy to this would be the Shell theorem in Newtonian gravity. If you're outside the earth's surface, you can apply the shell theorem to predict the gravitational field anywhere by assuming all of the earth's mass is concentrated at its center. This isn't physically true, but it's a useful mathematical trick. Of course, if you start digging towards the center of the earth, this solution isn't valid anymore. You have to recalculate the force of gravity taking into account only the mass contained within a shell whose radius is equal to your distance from the earth's center.

In the same way, you can solve Einstein's field equations to get a solution for a non-rotating, spherically symmetric object. By making an analogous solution to the shell theorem, where all the object's mass is concentrated at it's center, you can come up with a solution to these equations. This solution has an event horizon, or Schwarzschild radius. Obviously if this radius lies within the object, it doesn't really exist, since this solution is only valid outside of the object. I suspect that's the event horizon you're referring to. Solve the equations within the object, you should see that no horizon actually exists.

That the Schwarzschild radius does tells us is that if you take all the mass in your object and squash it to within the Schwarzschild radius, you do suddenly get a physical event horizon appearing. Because any force keeping the object from collapsing further would have to be communicated faster than light, it has to keep collapsing at this point, forming a black hole with a singularity at its center.