Because about 99% of the time the garbage collect is a negligible portion of your runtime at the benefit of a huge dollop of safety.

People really need to stop acting like a garbage collector is some sort of cosmic horror that automatically takes you back to 1980s performance or something. The cases where they are unsuitable are a minority, and a rather small one at that. If you happen to live in that minority, great, but it'd be helpful if those of you in that minority would speak as if you are in the small minority and not propagate the crazy idea that garbage collection comes with massive "performance penalties" unconditionally. They come with conditions, and rather tight conditions nowadays.

IDK about Fil-C, but in Java garbage collector actually speeds up memory management compared to C++ if you measure the throughput. The cost of this is increased worst-case latency.

A CLI tool (which most POSIX tools are) would pick throughput over latency any time.

Easy: because in your specific use-case, it's worth trading some performance for the added safety.