IMO, I believe that it’s easier to make friends at the beginning if the year. Although, you can still make friends later on. However, everyone’s looking to make new friends when they first move in.
Parties, dining halls, the gym, etc. = meeting people outside of your dorm and classes
The start of classes = Icebreakers
It’s also about timing and coincidence as well:
For me personally, I made fast friends with people in my building, some classes, and other activities. However, I didn’t find “my tribe” until much later on. I think for some introverts such as myself there’s pressure to find friends as fast as possible so you’re not at the dining hall alone, etc. My real friendships didn’t begin until end of first semester at best, end of second semester usually and continued on. There’s no formula to this.
Though you’re right OP it’s much easier to start connections with neighbors and classmates in the early weeks.