You might be surprised, but every game ships with dozens of known bugs. You have a static release date that is very difficult to change (when it's not impossible), and you don't have unlimited manpower to go through everything.
You fix as most as you can before the code freeze, then once the code is frozen you prepare a day-one patch, once again fixing most of the things you have previously caught and that have emerged after that. But even with that, you will have some issues left.
And that's assuming that every issue is "easy" to fix, and that every bug has the same priority as the other. What would you rather have, the money-in-peace-deals bug, or a ctd issue? The first is annoying, but you can play around it. The second, you can't.