Well, you're not exactly a salary worker in this case, you're more of an enterprenour, and everything regarding your product has repercussions, either positive or negative. If you stopped with the what ifs, it would have some effect on your earnings, and so would releasing main updates in 4 months instead of 6 (if you spent those extra hours working on the main game). Which one would be more beneficial to you, thats another discussion.
In the end of the day, it comes down to what I said before, you say working 9 hours on the main game would burn you out, while 6 hours in the main game + 3 hours on what ifs doesn't because you enjoy it more.
But "people need this explained" because it's pretty much the same work, and therefore there's not much reason why the main game would be taxing enough to be considered "work time", while the what ifs are "free time". But If the different script somehow makes it more enjoyable for you to work on what if, then it is what it is, I'm not gonna pretend to be able to read your mind.