Its in the first sentence KZ:

Eliminate Alchemy and Legendary Packs to simplify the experience, and leave less negative feelings if picking the “wrong pack type”.

Because of the changes in both the initial proposal and also this proposal there would be an impact on the value of the pack types. Its very hard to say ahead of time how much the changes would affect the different foils. So simplifying it for this set is a way to eliminate players from feeling bad if they picked the wrong pack type. However I think after the release of this set, going back to the additional pack types will be good for the next core set - since we will all have much more experience with how the conflicts worked and the value given to them.