Well I suppose that if you treat value types like a variation of an object reference rather than a variation of an object, then it would make sense that they cannot be mutated (since neither can object references but only their targets), with the added wrinkle of allowing such mutation during value constructors. To me this still feels less general than C or Go structs, which can have individual fields mutated in place (and even take the address of stack variables and pass pointers around, though that's unsafe in C and may require heap/GC allocation in Go unless escape analysis proves otherwise).
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Well I suppose that if you treat value types like a variation of an object reference rather than a variation of an object, then it would make sense that they cannot be mutated (since neither can object references but only their targets), with the added wrinkle of allowing such mutation during value constructors. To me this still feels less general than C or Go structs, which can have individual fields mutated in place (and even take the address of stack variables and pass pointers around, though that's unsafe in C and may require heap/GC allocation in Go unless escape analysis proves otherwise).