Ok... I am adding reasons as you want
@Muf-Muf:
1. Spells are only usable a bit on early stages, when increased income from single manufacture is giving a boost. Later in game players are having so much of Goods, boosts are not needed and increased income from boosted one manufacture is unnoticed, when player is having 4 or more of them. Same apply to Workshops. Many have 10 of them, so boost is eve more unnoticed.
2. This building only reason is to provide Spells, which are time consuming and as stated in point 1, their value is rather poor compared to their costs,
3. 3rd level only for diamonds. This probably will change with time, but if not, many players will stop at this point,
4. Building cannot be sold, what combined with point 3 will end as building on low level, not used by people, but without option of remove and regaining lost expansion,
5. Spells use relics and we don't have now source other than conquering provinces. Very limiting. Relics are taken also by Ancient Wonders. We didn't heard when will be introduced this new source.
6. It use a lot of place which is always very important. Now look at sizes of Faeries farms and realize how empty place is becoming precious.
7. It will be sitting in players towns unused, because it is having no real value or players will end at this quest and not go further - this is main plot
BLOCKER
8. There is no plans in a matter of months to improve it, so it will be crap for a months before it will be somehow improved. But after few months people will be waiting again for new race, because all current and available techs are to finish in a 2-3 months of regular play, without rush.
Enough reasons? Or maybe I should think more than 10 seconds to find more? This building is crap currently and making it obligatory is not a solution.