Many things can change over time.There is no other country in the world that will give people citizenship so easy, only after 3 years, so I don't understand why people would leave and not stick around to get it. What can you do with a PR card, and won't this expire at some point? Maybe people leave because they can't make it. The life is expensive and the funds they come with finish fast, or they just realize that they had better life before, or they are really unhappy.
The Canadian dream life of Rocky Mountains, Niagara Falls, health care, and social assistance does not work for everyone. Maybe if they made it easier
to acquire a visitor visa then some could see what it's really like before applying for a PR card.