The problem isn't fixing the bug. Good coders (and Bungie has loads of them, though apparently not in the "tools" department) can fix scores of bugs in a day. The problem is figuring out what the bug really is. Anything that's not 100% reproducible is nearly impossible to just go in and fix, because you don't really know what's causing the bug. Anything that is 100% reproducible still needs to be pared down to the absolute minimum number of steps in order to really figure out what's going on.

Let's take the Birth of History ship's glaring graphics bug, for example. Obvious bug, 100% reproducible. There's a giant hole in the middle of the ship; it's clearly unintentional since it lets you see out through the back of other textures on the ship. Obvious obvious obvious.

I'm assuming (based on comparison to other ships' graphics with similar components) that the problem is actually that the back part of the ship is too far away from the middle of the ship, leaving a gap. Seems like a really simple change to a z-coordinate value would solve the issue (or y coord or x coord depending on how they have things arranged).

BUT it could be that there is actually geometry at that position, and instead the texture is flipped (textures in Destiny are 1-way, as we've observed when we see through objects). They can't magically make all textures 2-way because then things like the pumpkin on your head would suddenly occlude your vision. So they have to figure out if the problem is the texture was created with the wrong side up (unlikely, since ship art is re-used and we'd see this problem on other ships), or added to this particular ship component facing the wrong way (again, unlikely, same reason), or if there's something special with this particular ship where the component was added in a unique way that messed up all the art (like the y axis values were inverted, which someone thought would make the component upside down, but actually made it inside out).

OR maybe all of the art assets are totally fine on the ship. If you load the ship up on its own using the dev tools that take overnight just to load a map because god damn stupid tools design that makes patching the game take forever UGH BUNGIE YOU KNOW BETTER, the ship is just fine. Like totally fine. Which means the missing art has to do with some kind of weird interaction with other elements in the game. Probably the UI, like they share texture memory space, and the UI code guarantees that it always wins when there's a conflict. This would be a problem for that texture with that particular color pallette (which is, afaik, unique), but would not necessarily be easy to fix because artists don't generally dictate how texture memory allocation occurs, but - rather - the core engine figures it out on its own. So you'd need to figure out why the core engine is making this mistake and then re-write the whole core engine and hope nothing else broke in the process. This is also unlikely, because bad gfx engine code tends to cause far more problems than one single isolated missing texture.

So if I'm being totally honest, it really does seem like the only reason there's a hole in that ship is that Bungie is being lazy as hell fixing a pretty basic art issue of misplaced assets. Seriously guys, you only have to change one number.

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But I digress. Sometimes the bug is really difficult to parse. You have to capture the event live, using a dev kit that you can then interrupt and go back to look at what procedures called what other procedures and where the decision to do the buggy thing came from. So really really really rare bugs like this one are pretty tough to figure out. It's actually easier to do since the game is live and you get more instances of the bugs occurring, but still very hard.