Assuming you mean this: https://docs.microsoft.com/en-us/dotnet/csharp/language-refe... it looks like a restricted form of the C preprocessor. (We may quibble about whether it is separately "pre" processed or not, but even cpp doesn't run as a separate stage in modern C compilers).
The C# preprocessor is unnecessarily restricted. It has a few features but it feels very arbitrary what they include or exclude. I think they didn’t like the idea but couldn’t avoid it totally so they did something half assed. I bet a lot of frameworks that need reflection could be replaced with macros if the preprocessor had a few more features.
It is not half assed, rather what has been proven since the 60's to work properly in all languages that aren't C, nor copy-paste compatible with C.
Even C++ is reducing the need to keep using the pre-processor with each ISO revision, in an ideal modern C++ world without C legacy baggage, the pre-processor will be so half assed like in C#. C++20 is already almost there.
The C pre-processor doesn't have the monopoly on conditional compilation, it wasn't even the first language to support such features, they were already available in Algol variants and Macro Assemblers.
Fair enough, but C is the snowflake here, in other languages conditional compilation is part of the language.
Actually even in ISO C, the pre-processor is not required to be separated from the language, it is just kept that way in most compilers due to how C was originally implemented.
