You are missing the point. Other meeples can
also go in the Cathedral in the City, but the Abbot can
only go in the Cathedral, since the features it can claim are only religious institutions (e.g., Monasteries, Gardens, Shrines). Therefore, the Abbot is restricted to the Cathedral, whereas other meeples can go elsewhere in the City (some with their own restrictions). A longer list of restrictions is listed later on the page:
The following figures can be placed in a district of the city of Carcassonne:
Normal meeple, the standard option (Base game)
Abbot, only in the cathedral (Base game - The Abbot)
Large meeple (Exp. 1 - Inns and Cathedrals)
Wagon, not in the market (Exp. 5 - Abbey and the Mayor)
Mayor, only in the castle (Exp. 5 - Abbey and the Mayor)
Ringmaster (Exp. 10 - Under the Big Top)
Phantom (The Phantom)
The reason the Abbot is called out twice is because it is included in the base game, so requires immediate clarification. The others are expansion components, so they are only clarified in their own expansions.