I think many people aren't pointing it out because they don't have a problem with it. Since 2009 we've learned that they keep cropping up earlier and earlier in the timeline, and some people have a problem with this, while others don't. There's nothing specifically stated in the first film that contradicts anything that's happening now or then. ROTF even has a statement saying that they've been around a lot longer than Sector 7 believed, but didn't want to investigate.
I don't see anything wrong with the Transformers having always been there in hiding on Earth as long as The Last Knight manages to make sense of all the different plots and how they fit together. The connection between 2 and 3 and 3 to 1 is really where things are the wonkiest, and as long as this new movie touches on that and tries to make sense of it, I'll be fine.
That's something from a video game that probably doesn't have anything to do with Transformers at all.