I guess more specifically, why can't I write C++ in C#.
As a side note, the i7 4770k produces somewhere in the region of one hundred thirty-three billion seven hundred forty million operations per second. 8GB is sixty four billion bits.
We don't really need micro optimisations and bitflags anymore. Premature optimisation causes loads more problems than it actually solves. That's why we have languages like Java and C#.
https://en.wikipedia.org/wiki/Instructions_per_second