It only became a trio as time went on. Randy survived the first film. Cotton survived the second film.
I mean yeah it's kinda cheesy that there weren't any major deaths in 6 but I still like the movie a lot, and I suspect the plan was they were saving it for 7. I think 5 hit pretty hard so I'm fine with a little breather in the middle of a hypothetical trilogy
It's just a play on the trope of in these types of ensemble horror movies that it's safe to bet the main cast is safe which you can then subvert in later sequels. Probably mostly a play on Stranger Things at this point.
Pretty sure they stepped up because the franchise was dead in the water after they fucked up and lost their new stars.
I wouldn’t be surprised if they did approach her in a respectful, but insincere, way. If they didn’t convince her to come on board they would have nothing to carry the next film. They probably begged. Too bad they only did it under the current circumstances.