I just really needed a string library written in C, and it didn't seem as though there were many options. The first thing I found was the Simple Dynamic Strings library, but it wasn't maintained and depended on GCC extensions, so I decided to write my own. After getting a basic functional concatenation, I benchmarked it against std::string to see how slow it was, and to my great surprise, it was actually faster. From that point, I realized I can actually write some pretty fast code, and I decided to make the library centered around that.
I'm surprised to hear it was faster, I just assumed C++ standard library is optimized for speed since I thought that's what C++ is known for compared to JavaScript.