We were looking for something easily embeddable, but all host modules were provided by the application, so there was no need for outside C extensions. And the set of libraries that was importable was restricted and coding styleguides banned advanced language features like metaprogramming, so we could afford to cut corners on corner cases of the language. "Decent" performance (i.e. more like Java than CPython) was a requirement, as was multithreading support and lack of a GIL, and RAM usage was also at a premium (which was probably the largest argument against PyPy...also, this was a couple years ago, when PyPy was not as mature).