It's backwards. Writing a C compiler in C or Asm makes sense, a Python compiler in C also does, but a C compiler in Python is an odd inversion of abstraction.
I guess this harkens back to the days when you had to write a compiler in a low-level language because that’s all that the platform that you are targeting supports. Then it sounds weird to talk about writing a compiler in a high-level language in order to target a low-level one, because surely these high-level languages are more platform-dependent than the blessed (guaranteed on the platform) low-level one.
But these days we can access dozens of languages on many platforms. And we can use high-level languages that are good for writing compilers—languages with good string types and algebraic data types—instead of being limited to awfully imperative/procedural ones.
In other words: your perspective sounds way more anachronistic.
Why? The objective is to translate code in one language (C) to another (machine code or assembly or perhaps an intermediate representation). Why does it make sense to use C for that task and not Python or some other language? It's not like C provides facilities that specifically enable compiler writing or text parsing for itself that other languages are lacking.
But these days we can access dozens of languages on many platforms. And we can use high-level languages that are good for writing compilers—languages with good string types and algebraic data types—instead of being limited to awfully imperative/procedural ones.
In other words: your perspective sounds way more anachronistic.