They want to socialise and be entertained.
An important thing to remember is that, as a developer, you are often in control. In many cases you are completely controlling what your players do and how much they spend (mobile industry is really good at this in a bad way.)
Just do something interesting that makes them feel good - give em some of dat dopamine.
Things you could do:
- obbies
- exploration
- secrets (achievements)
- easter eggs
- practice areas
- hangout areas
- minigames