I've heard before that an extension of string field theory to M-theory doesn't exist, or at least is very unlikely to exist.

Why is that? I assume it has to do with the spacetime structure of M-theory, but that, as far as I'm aware, isn't set in stone. One could always have a field theory on a non-commutative spacetime, but I suppose one could argue that this isn't an *extension *of string field theory.

I don't have much understanding of M-theory, but then who does? To be clear, I'm not asking why we don't *currently *posses such a theory, since M-theory seems so poorly understood as it is, but is there a fundamental reason why we shouldn't expect a field-like formulation?