Yeah, that's a good point--- Lua is another example of an MIT/BSD-style licensed embeddable language that in practice doesn't seem to have produced proprietary forks.
I've heard about several in-house forks of Lua, but usually, they happened because companies settled on a specific version (e.g Lua 4.0) and imported it into their project. Lua's small enough that maintaining a private fork of the whole language is reasonable, though.
The only public fork of the whole language I've heard of is Metalua, though.
