For sake of example: a "locale-aware" number conversion routine would be the worst possible choice for parsing incoming network traffic. Beyond the performance concerns, there's the significant semantic difference in number formatting across cultures. Different conventions of decimal or thousands coma easily leading to subtle data errors or even security concerns.
Lastly, having a simple and narrowly specified conversion routines allows one to create a small sub-set of C++ standard library fit for constrained environments like embedded systems.
Lastly, having a simple and narrowly specified conversion routines allows one to create a small sub-set of C++ standard library fit for constrained environments like embedded systems.