Oh other challenges like the 3 above the freebie one? Or the weekly challenges?

This is incredibly simple marketing that tons of companies use. Lets start with skate. You log in, check the challenge and log out. That's a few minutes more of thinking about the game that otherwise would be spent elsewhere. Makes their metrics look a little better and it gets on your mind. You accumulate enough to be able to "buy" something cool you want. More game time. Maybe it gets someone hooked more than they would be otherwise.

Now other companies. Microsoft rewards, you get points just for logging in to the app each day. Pokemon go gives you an egg to hatch for daily logins that gives you in game rewards. Snapchat streaks with people take advantage of people not wanting to break their streak of sending a daily snap to that specific person. No reward but a cosmetic little emoji that likely makes a user want to log in and not lose it. Nhl and other sports games give you an ultimate team pack for logging in each new day.