C is low level for at least one reason: manual memory management. Especially with modern hardware, memory management is at the center of programming. For example, Rust prides itself in being memory safe without a garbage collector, memory management is more or less the entire reason for Rust to exist. Why is C fast? Memory. Why is C unsafe? Mostly memory. One of the big reason parallel computing is hard? Concurrent memory access. Functional programming is often surrounded by plenty of mathematical concepts, but a good part of it is to pretend that objects are immutable when behind the scenes, the compiler works with mutable memory.

In C, every call to the allocator is explicit, that is, if you are using an allocator at all. Compare to oldschool C++, with new/delete and raw pointers, where you may call the allocator explicitly, but still, a lot happen in destructors, automatically. In modern C++, with smart pointers, it is essentially like a garbage collected language in the sense that allocation and deallocation all happen automatically.