Most people who write code in C are not that good at avoiding memory safety issues. The process is mostly to write some code, run it, then fix it until it doesn't crash immediately anymore.
Have you ever been the first person to run valgrind on a codebase? Lots of uninitialized reads and use-after-free issues will be flagged, because they don't normally crash the program and therefore go undetected without using an additional checker.
It can be fun to watch the error messages flow by, until you realize that now you have to file tickets for all of them. And some people won't even see the problem with those errors that don't crash the program, because potentially exploitable vulnerabilities are not as obviously bad as crashes.
Btw, I am not a C fan, in fact I think I have no favorite language, I use what I have to for the project
The time and effort to secure a C program against malicious input is absolutely huge. It would be quicker to write a secure dsl that using raw C. Which brings us back to scripting languages that have that implemented already as a library you load to run your requests through.
Also what is the point of calling out on projects that are not using "cool" languages? You don't agree with the developer choice that is OK, probably that developer does not agree with your choice and has other priorities and if is an open source project probably he wants also to have fun while coding it.