You study a college, everyone has a Facebook account so it makes sense for teachers to just notify students through Facebook. If everyone has a Facebook account and you dont, its your problem. Noone is going to message you via email just for you.
A different example, You go to an Office. There is a huge notice board. Its filled with notices and there is a huge queue. The office management has not made it digital so the staff members themselves setup a Facebook page and post the pics of notices. Because they know how to use Facebook and everyone around them use Facebook. So what kind of fool would reject that convinience in looking up notices and go queue up in there?