My high level understanding of the UB concept is, that it means false positives to the question "Is that a valid program?". Given that the philosophy of C is mostly "Do what the programmer wrote, no questions asked.", it leads to designing the language so, that the probability of false negatives goes to zero. This obviously means, that the number of false positives goes up.

Rust basically takes the opposite approach of making false positives go to zero, which makes the false negatives go up, which you need to work around with unsafe or type gymnastics.

The third approach is to make both false positives and negatives be zero, by restricting the set of programs, which is what non systems languages do.