Many would only care about and count their liquid assets - which the 2nd pillar isn’t. 
Well, most 20-year olds have just begun working. I can kind of understand that they want prefer to treat themselves to something nice after earning their first own “proper” money.
To be fair, many 25 or even 30 year olds won’t have much in their 2nd pillar (retirement savings are only becoming compulsory at 25).
Even for me being a bit older, 2nd pillar makes up only about one seventh of my net worth (only half of what I’m holding as much in pillar 3a, even without ever having been self-employed).