You may not only care about portability. And "safety" sometimes also means being able to meet realtime requirements, and also often means having the ability to carefully account for resource use in ways that many interpreters does poorly (and no, kernel enforced system limits are not always an option).
Many interpreters also make assumptions (e.g. expecting a POSIX'y system) about the host system that many embedded platforms doesn't necessarily meet.
I've more than once looked at interpreters for embedding and found most of the alternatives sorely lacking. Very few interpreters are well suited for embedding on constrained platforms at all (Lua, admittedly is probably one of the more solid exceptions). And once you start having to write lots of support code in C to port or sandbox your interpreter of choice, the reason for considering an interpreter quickly becomes less compelling.