That's not true. Wube is working of a big Factorio 2.0 style update. They push updated on what they're doing every other Friday, and they all go in detail and are very interesting.
Factorio 2.0 will shine brighter than ever before. Also, there is murmurs of possibly open sourcing faction later in the lifecycle.
Well, kinda the same price, they sometimes up it to account for inflation. I do see the DLC difference (this could be said to be an equivalent of for example Minecraft Dungeons with the amount of content, but I see how it is kinda "more of the same").
Anyway, the 2.0 update does bring a lot to the base game for free.
And it's definitely worth the money! Just odd. I fully expected them to develop Minecraft 2 and 3 years ago to cash in and overwork some of the basics but that didn't happen for better or worse, but probably better. It remains to be a truly unique game till this day.
That's definitely just a spin-off. It's an entirely different genre of game and was never intended to be sequel. Same goes for the choose-your-own-adventure one.