The original C committee wrote, as part of its guiding principle to “Keep the spirit of C”, that “To help ensure that no code explosion occurs for what appears to be a very simple operation, many operations are defined to be how the target machine’s hardware does it rather than by a general abstract rule.”¹ That is, if you write `a = b + c` you expect the compiler to generate an `add a, b, c` instruction, and if that happens to trap and burn your house down, well, that's not C's problem.
I'm convinced that the original UB rule was intended to capture this, and the wording was an error later seized by compiler developers. As evidence, consider Dennis Ritchie's rejection of `noalias` as “a license for the compiler to undertake aggressive optimizations that are completely legal by the committee's rules, but make hash of apparently safe programs”². If anyone at the time had realized that this is what the definition of UB implied, it would have been called out and rejected as well.