Because everything always changes, and you will not see the world exactly like you do today, on another day.
The changes might be slow and subtle across time, but you will change as will the environments you are situated in.
Why do you need a reason when you can just let yourself be here now. Acknowledge the moment. Keep doing this. Still your mind. Just be here. Whenever you reject the moment, you become unconscious. Just let yourself be conscious to the now.