> So the question I have for hardcore low level programmers: why don't they invest more on the memory allocators
A partial answer is that part of low-level programmers avoid memory allocation and threads like plague. In some cases they are not even an option (small embedded programming, it's nearly as low-level as you can get before going hardcore for real with assembly programming), but when they can the keywords are efficiency, reliability, predictability, and simplicity : statically allocating in advance is a thing you can do because the product is typically with max specs written on the box (e.g. max number of entries in a phone book, to take a generic dumb example), and you have to meet these requirements even if the customer uses all of the capabilities to the max; no memory overbooking allowed, which is basically what dynamic allocation is, in a sense.
> instead of starting a new programming language
If I were to start a new low-low level programming language, I would basically just fix C's weak typing problem, fix the UB problems that only come from issues with long-gone processors (like C++11 finally did with sign encoding), "backport" some C++ features (templates? constexpr?), add a pinch of syntactic sugar and fix union types to have proper sum types. But probably I've just described D and apparently a significant chunk of C23.
A partial answer is that part of low-level programmers avoid memory allocation and threads like plague. In some cases they are not even an option (small embedded programming, it's nearly as low-level as you can get before going hardcore for real with assembly programming), but when they can the keywords are efficiency, reliability, predictability, and simplicity : statically allocating in advance is a thing you can do because the product is typically with max specs written on the box (e.g. max number of entries in a phone book, to take a generic dumb example), and you have to meet these requirements even if the customer uses all of the capabilities to the max; no memory overbooking allowed, which is basically what dynamic allocation is, in a sense.
> instead of starting a new programming language
If I were to start a new low-low level programming language, I would basically just fix C's weak typing problem, fix the UB problems that only come from issues with long-gone processors (like C++11 finally did with sign encoding), "backport" some C++ features (templates? constexpr?), add a pinch of syntactic sugar and fix union types to have proper sum types. But probably I've just described D and apparently a significant chunk of C23.