The slab allocator is a great strategy, but of course only works for memory, which is really a special case of one out of all of the resources we want to manage

The slab allocator is a great strategy, but of course only works for memory, which is really a special case of one out of all of the resources we want to manage. If you're writing long running processes you need to care about any number of file descriptors, maybe mutexes, certainly locks. You can't bypass all of this in all cases assuming that you only need to deallocate memory. Destructors tidying this up as the exception unwinds the stack is extremely easy to reason about and stops any number of idiotic mistakes.