It really is not that complicated of an issue. First off:

Why does a Gravitational Wave escape the Black Hole and Not Light?

Light is a form of particle that has a ridiculously low amount of mass. This particle moves in a certain pattern based upon the weight it has going at its intense speed it is heading at. This intense speed is influenced by what it is speeding through (light is faster through a vacuum than it is through cement when it does not bounce off)

Gravity however for how it works is best described as “like a well”. Like a sloping structure that gets much more steep as it gets closer to the center of the well. To follow a gravity well you have to switch to a 2d slice of how the world works (as looking at a gravity well in 3d is… a bit hard to look at easily)

It should be noted that the Gravity wells never actually end. They’ve just “ended enough to not really care about”. This is without taking into account LaGrange Points — which still have effects from other gravity wells — but it is so negligible it is not taken into account.

When these two black holes smack into each other… you essentially have two gravity wells bumping into each other in a really violent manner. This ultimately cases a bit of distortion of how the “gravity well” stuff looks extending out from the two gravity wells violently colliding into each other.

As these two gravity wells warp into a single one — we have a total of three gravity wells to deal with for how things are managing within these three.

None of these gravity wells actually end. Two are no longer there after that. One is the final one.

As much as it would be much more clean if the difference in gravity was something instantaneously found all through out the universe… but it wasn’t. The effects of how the third gravity well take a while to proliferate throughout the universe.

The gravity wave — as described by the two black holes collapsing into a single black hole — is pretty much an update of the topography of physical orientation of the universe itself mitigating out from the event. Specifically the topography of the gravity wells, not the actual gravity wells, just the practical gravity wells (which is much more useful of information for us right now). Which is one of those things that is hard to properly track of — outside of 2D slicings with the origin of those slicings being the centre of said galaxy wells.