Well, Google has 100s of millions of lines of C++ that power much of the internet. They certainly have no intention of getting rid of this code, and have deemed the tradeoff worthwhile. Yes, in theory this C++ codebase might not be the most reliable or secure, but their practices are certainly scalable and battle tested. Not saying it is easy, but it is certainly possible to build an ecosystem around C++ with fuzzers/linters/whatever to reach an "acceptable" level in practice.
> Meanwhile, huge amounts of quite safe Java and C# code keep happily ticking along -- exposed to the internet -- often needing patches only for the C/C++ modules that they include as a part of some framework!
Not necessarily. Plenty of null pointer exceptions in production Java code that bring down systems. Yes, they are "safe" but I don't think the tens of millions of customers affected appreciate such subtle nuances: the consequences are the same for them.
I agree that there can be more severe consequences due to the lack of "safety" from exploits, privilege escalation, and what not. But with stuff like sandboxing, the broader ecosystem, etc the decision isn't as simple as your argument might suggest.