The reason behind this is that as with the AW researches it was always intended that these researches should be mandatory, as Magic Academy/casting Spells is seen as a core part of the game, just as the Trader or Barracks, or Builder.
A little bit off-topic, but I'm going to make the wild guess here that the mandatory quest to build a barracks is going to remain mandatory forever. Ergo, I will never play through any of the storyline quests. That's sad news, but I expected that many months ago.
Back on-topic, the game developers have once again (forcefully) proven the direction this game is meant to take: research, build and play however you like - just as long as it's how we want you to.
In all honesty, there's nothing wrong with that. The devs have a clear image of what they
want and
can offer us, as well as where they want to take us in the future. Unfortunately, that future is starting to become such a narrow path, that I'm starting to wonder whether I'm going to continue to fit on it, or just fall off.
The last update had one of my most active neighbours quit the game due to the number of provinces required for unlocking the next chapter. This update has made another neighbour of mine consider quitting because they are being forced to research techs they do not want to. I have often considered quitting because I'm stuck on a mandatory quest to build a barracks that I have absolutely no use for.
...there appears to be a trend here.