You could’ve just watched the MTGGoldfish video on the deck but fine, here we go:
• Teferi says you can only cast stuff only at the same time as sorceries.
• The Comprehensive Rules define sorceries as shit that you can cast “during a main phase of their turn when the stack is empty” (307.1).
• Knowledge Pool makes it so that you can only cast crap via its effect, meaning while the Knowledge Pool trigger is still on the stack i.e. NOT as a sorcery/at the time a sorcery could be cast.
As you can see understanding why this combo works requires digging into the guts of the way Magic operates under the hood. But you cannot dispense with this complexity of Magic because otherwise the game doesn’t work anymore. There has to be hard, unambiguous logic underneath the mechanics or else you couldn’t program rules engines the likes of which enable stuff like MTGO or Magic Arena.
You might dislike how this rule plays out in this instance but if you changed it to something that you perhaps consider more intuitive (wow, am I ever still salty about that dumb fucking rules change concerning planeswalker damage redirection after Dominaria). However, I can guarantee you that any change you make will inevitably lead to other situations where you can arrive at equally unintuitive card interactions.