I've worked on many large projects in C++, and every single one of them contains a bespoke, buggy, undermaintained JSON parser, URL parser, configuration file parser, async framework, and so on. It used to be the case that almost every large C++ project started out by defining its own friggin' string type.
Dependency anxiety is a variant of NIH syndrome, and it leads to much, much worse quality software in the average case. Most companies are not in the business of writing a bug-free async framework, and yet here we are. The cost of vetting your dependencies is much, much lower than writing and maintaining all these things from scratch.