Programmers make stupid mistakes in the safest languages too, even more so today when software is a career and not a hobby. What does it matter if the memory allocation is safe when the programmer exposes all user sessions to the internet because reading Dockers' documentation is too much work? Even Github did a variant of this with all their resources.
Because memory vulnerabilities don't make programs immune to other dumb mistakes. You get these vulnerabilities on top of everything else that can go wrong in a program.
Manual checking of memory management correctness takes extra time and effort to review, debug, instrument, fuzz, etc. things that the compiler could be checking automatically and reliably. This misplaced effort wastes resources and takes focus away from dealing with all the other problems.
There's also a common line of thinking that that because working in C is hard, C programmers must be smarter and more diligent, so they wouldn't make dumb mistakes like the easy-language programmers do. I don't like such elitist view, but even if true, the better programmers can allocate their smarts to something more productive than expertise in programs corrupting themselves.
Because memory vulnerabilities don't make programs immune to other dumb mistakes. You get these vulnerabilities on top of everything else that can go wrong in a program.
The issue is that these great new tools don't just fix the old vulnerabilities, they also provide a lot of new, powerful footguns for people to play with. They're shipping 2000 feet of rope with every language when all we need is 6 feet to hang ourselves.
There has been a bunch of failed C killers, and C++ has massively shat the bed, so I understand that people are jaded.
However, this pessimistic tradeoff is just not true in case of Rust — it has been focused from the start on preventing footguns, and actually does a great job of it. You don't trade one kind of failure for another, you replace them with compilation errors, and they've even invested a lot of effort into making these errors clear and useful.
