> Malloc and memory allocation methods are at least 10k+ lines of code for instance.

Only the really big ones, e.g. here is Emscripten's allocator that focuses on small binary size and is implemented in about 1.5 kloc (ignoring comments and whitespace it's actually under 1 kloc), and that allocator is perfectly fine for most use cases (especially C code bases which typically don't have a high allocation frequency):

https://github.com/emscripten-core/emscripten/blob/main/syst...

...and Seb Aaltonen's offset allocator (used for allocating GPU buffers in his Vulkan API wrapper) has under 500 lines of code:

https://github.com/sebbbi/OffsetAllocator/blob/main/offsetAl...

Right tool for the job etc... big general-purpose allocators like jemalloc or mimalloc are usually a bandaid to somewhat salvage a failed memory management strategy.