I have heard this explained as stuff that needs to be done yesterday almost always also has the property of cannot be disrupted for any reason (which is why it was so urgent to begin with). So your quick hack that stops the world from exploding cant afford to be meddled with, lest it causes the world to explode in the process....
Its similar to the worse is better philosophy, low quality wins because it can be churned out quickly, it stays in place because the value proposition of replacing it is unclear or insufficient.
When it comes to critical things, its very important that changing things has a definite, demonstrable purpose in regards to its outward effects, not just itch scratching. Aesthetic concerns matter little because the potential for disruptive effects is a near certainty while the upside is much more nebulous typically (the devil you know etc)