The version with the -ing form has the same sense as your rewrite. The only difference is the syntactical relationship between two sentences.
- Available MATLAB features [...] help programmers [...] and allow high expressiveness [...].
- Thus they contribute to enhanced productivity.
Your version is a complete sentence, which must stand apart from the previous sentence: a period or a coordinating conjunction or a semi-colon must come between them.
However, it seems that the author wants to make that second sentence the climax of a single longer sentence. To accomplish this he rewrites it as a subordinate clause:
- The finite (tensed) form contribute becomes the non-finite form contributing
- The subject they is deleted because it is understood to be the same as the subject of the ‘superordinate’ sentence in which the subordinate clause is now ‘embedded’.