i have little recall how smogon grammar works but the following makes sense in my head and i wrote most of this up hours ago so my thoughts are disjointed, i don't quite recall if I had a finisher sentence, and i'm unsure if my thoughts are there in full.
STAB needs to be paired with a variable - by itself, it doesnt make sense. "swampert's same type attack bonus deals good damage to heatran", a good player will place the "move" or "attack" right after 'same type attack bonus' but relying on the reader's mind to be knowledgable enough in both the english language and competitive battling is not always the case. if it was "swampert's STAB deals good damage to heatran" then STAB becomes a noun, something tangible swampert has access to that it itself can deal good damage to heatran, which is not the case
"swampert's same type attack bonus Water-type deals good damage to heatran" is technically correct I think, it just reads weirdly. when you make it 'STAB' it becomes more natural to read
I'm not sure what your issue is, CP?
"Fire-types such as Infernape and Heatran can deal a lot of damage to Ferrothorn with their STABs" - the STAB's variable is Fire-type. its talking about any attack that is fire-typed. sure, we'll never recommend fire fang heatran or flame wheel infernape, but these are things that are included in that sentence. The word "move" is never mentioned, because it doesn't talk about anything specific, it's discussing the entire arsenal of Fire-type moves the two Pokemon have at their disposal.
I would personally rewrite the sentence, however. "Infernape and Heatran can deal a lot of damage to Ferrothorn with their Fire-type STABs". With this sentence structure, instead of the reader having the read in between the lines to understand that Infernape and Heatran gain STAB from Fire-type, which would require (what they hopefully already have but better safe than sorry) a basic knowledge of what STAB is. Now, the information that Heatran and Infernape are Fire-type is the information not clearly present in the sentence, which is (in my opinion) the way it is better written.