I think understanding roughly how Malloc works can be very helpful in pretty much any area where performance becomes important. Without knowing a bit about Malloc it's hard to understand the benefits of SLAB allocators and similar (which are used everywhere from game engines to OS kernels to DBMS etc).
In it's most basic form Malloc basically is a linked list.
Even the nature of a Struct, and how it might be more efficient than an Object, and the difference between a Stack and a Heap... All that's pretty accessible without sitting through a course on the finer workings of malloc.
The memory is there. It provides my byte buckets. I don't need to care much beyond that to be a good web-developer.
Asking most developers about malloc is probably about as relevant as asking about video frame-buffers. For some spaces it's make or break, but for most it's just useless trivia.