The reason that this wasn't done is that we believed (and it still seems to be true) that you cannot make C or C++ be memory safe at compile time. Or rather, you cannot do it without introducing backwards incompatibility, which means you're effectively making a new language anyway, and something that's a non-starter for those languages. (as it should be, IMHO.)

It had nothing to do with "sexy" and everything to do with engineering goals. I assure you, a lot of work in Rust is dirty, political, and not sexy too :)