Because it directly contradicts the "only 20% of your code is performance sensitive and the other 80% can be scripting language X" nonsense that scripting language apologists constantly parrot with no evidence. This is a good example of how scripting languages are in fact not well suited to application development, and should instead be used for scripting.
The question isn't how much Python there is relative to C++, the question is how much C++ there would be if there were no Python.
To put it more concisely: "only 20% of your logic is performance sensitive and the other 80% can be encoded in scripting language X leading to a significant reduction of your total code."
It doesn't lead to a significant reduction though, it is hardly any reduction at all. Look at their code, the python could be replaced with C++ at an almost 1:1 ratio.
I would argue that BIND isn't "merely" an application: it's almost kernel-level in what it needs to do and how it needs to respond. At a minimum, it's system-level—but definitely not application-level.
There is nothing almost kernel-level about it. It is an application. You seem to be trying to draw a very arbitrary distinction between applications and applications that you want to consider special for no particular reason.
Because it directly contradicts the "only 20% of your code is performance sensitive and the other 80% can be scripting language X" nonsense that scripting language apologists constantly parrot with no evidence. This is a good example of how scripting languages are in fact not well suited to application development, and should instead be used for scripting.