Comment by manyworlds

Generally kernel code is also written to specific constraints. Out-of-tree drivers are usually bad at conforming and hypothetical out-of-tree webassembly drivers would be bad for similar reasons. Memory safety isn’t enough, using kernel interfaces safely requires conformance that webassembly can’t statically guarantee like BPF can

Basic examples: code that takes a lock and never releases it, code that loops forever, code that leaks kernel resources.