It's not just backwards compat, it's all the crazy guarantees that the stdlib has to make. Most code doesn't have strong exception guarantees... the stdlib gene

It's not just backwards compat, it's all the crazy guarantees that the stdlib has to make. Most code doesn't have strong exception guarantees... the stdlib generally speaking does. It also has to deal with all sorts of silly things without breaking like people overloading operator,() and still expecting things to work without issue. They really are a case study in getting decent performance in most cases out of exceptionally defensively written code.