Answer:
the focus strategy was imitated.
Step-by-step explanation:
Based on the information provided within the question it can be said that in this scenario Micheal Porter would explain this as the focus strategy was imitated. This is because the focus strategy that Bob and Shirley implemented in order to satisfy the need for people needing a place to stay was copied (imitated) by their neighbors who managed to take many customers away from Bob and Shirley, which is why they could no longer book all their rooms.