Because the amount of code already written in C is astonishing and that's just counting stuff that is in the public sphere. Once there isn't a dependancy on C-

Because the amount of code already written in C is astonishing and that's just counting stuff that is in the public sphere. Once there isn't a dependancy on C-programs or code then C will be obsolete. Now the task comes to rewriting hundreds of thousands of hours of code to make it so that the rust backends for systems are up to spec with what's already layed down. C is popular because a lot of stuff is written in it and it's the obvious choice due to the tooling for certian tasks.