What makes a common programming language non-context-sensitive but RE?
I think you are conflating syntax and semantics.

A formal language is RE if it is possible to recursively enumerate all valid "sentences" (read "complete programs"). Validity here effectively means only that a compiler could convert the program into an executable, without saying anything about what that executable does.

That has basically nothing to do with the semantics of the program. We could design a programming language which is arbitrarily difficult to parse, but whose semantics are simple enough that the generated executable is guaranteed to be a complete function. (Removing all looping constructs is a good start.)

On the other hand, we could design a language which is trivial to parse, as are most stack languages, but whose semantics are effectively Turing complete (aside from the finiteness of memory in a physical realization of a processor.)