> See zero initializing variables by default

Strictly speaking the standard only requires some pattern that is not tied to program state. Zero works for that, but so do other static patterns like 0xABAB... or the like.

> (WHY?)

The motivation section of the corresponding paper [0] might be interesting. tl;dr: it lets wrong code be wrong without suffering from (all) the consequences of full-blown UB.

[0]: https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p27...