Think of a hostel as the home you grew up in as a child. There’s the bedrooms, the bathroom, the kitchen, the dining room and the living room and instead of your family, there’s a “family” of fellow travelers.
In essence every room of the hostel really is a common area. Sure, you’ll lounge on the couches in the common room with other guests but you might also find yourself preparing a meal together with someone in the kitchen or maybe playing cards with someone else on your bunk in the dorm.
The point is – hostels are setup to connect people so take advantage of it.