I think the difference is in the difficulty in preventing the bugs. I'd be very surprised if our codebase at work contained SQL injection bugs. We use a library that protects against them by default, and all code gets reviewed by a senior developer. SQL injection is easy to prevent with a simple code review process.

Subtle issues with undefined behaviour, buffer overflows, etc in C are much trickier and frequently catch out even highly experienced programmers. Even with high quality developers your C program is unlikely to be secure.