Scheduling stuff with friends does not preclude also having spontaneity. It's just that for busy people spontaneity doesn't happen often enough to maintain a friendship.

Spontaneity doesn't happen unless you have lots of extra time lying around and most busy people don't have that.

In fact ironically I actually have to schedule blocks of unscheduled time for myself and schedule blocks of unscheduled time for time with my partner. Those blocks of time just mean that I don't have a specific plan and will do whatever I/we feel like doing when we get to that time. That allows for spontaneity in the context of me alone as well as in my relationship.

However, for friends that doesn't really work so well. It's not like if I have a block of unscheduled time that a friend is just going to magically knock on my door (I don't live in a college dorm, but if you do, that might work.) For friends we kind of need to agree on e.g. where to meet or what to do, so for friends it's usually scheduling scheduled time.