[jandrewrogers]

The containers in the STL have issues due to the limitations of C++ when they were designed, catering to the lowest common denominator user, and simplifying things for implementors. It is not uncommon to find cases where the STL is a poor fit or annoying to use due to its implementation and design details. In the case of modern C++, you also have the issue that the STL containers aren't designed to be used in an advanced metaprogramming context, because they pre-date that being an intentional part of C++. Some of this is unfixable because backward compatibility. Also, C++ is commonly used in contexts where performance is critical, so the optimality of the STL for purpose matters more.

Some of the common issues: static allocation or lack thereof, requiring default constructible classes, initializing memory you are going to overwrite anyway, inability to be used in some metaprogramming contexts, suboptimal allocation behavior, etc. The STL is opinionated but unfortunately that opinion dates to a time when C++ was primarily used for ordinary app development, not high-performance code.

Like many, I maintain my own C++ "standard library" that is much better designed for the kinds of software I tend to work on (database kernels and data infrastructure, mostly).