There’re indeed multiple third-party libraries for that in many languages. E.g. for C++ we have lubuv, boost.asio, etc. However, built-in solutions have upsides

There’re indeed multiple third-party libraries for that in many languages. E.g. for C++ we have lubuv, boost.asio, etc. However, built-in solutions have upsides. They work out of the box i.e. deployment is simpler. They’re integrated into the language, e.g. most network IO in golang is asynchronous under the hood, compiler and runtime do that automatically. They’re integrated into standard libraries, e.g. in .NET all streams be it files, sockets, or transforms like compressors and encryptors support asynchronous operations. The support is usually better, too.