Distribution of Zwifters by 20min w/kg

I wonder to what degree these will be configurable. Will the wattage floors/ceilings be decided upon by a community race organizer? How would these be determined, eg. if you want a Cat for 2.7-3.0 what’s the correct wattage floor?

This may be a superfluous question, but why did it become a game rule like blackjack?