Amenity spaces are a requirement for multi-residential development (anything over 3 units in a building). Whether they are common or private is up to the development authority to determine for townhomes and rowhouses, and if there is more than two semi’s on a parcel.. and if the use is discretionary.
Apartments usually have balconies provided so common amenity spaces are not required - but more a marketing scheme to get people into their units (likely less needed under existing market conditions, but a great sell in down times which there will be in the future). Apartments are also generally required to go to CPC and Council for decision, so there’s that, too.