Many of the online courses, at least in TDSB, generally don’t start on day one of the semester, they wait a few days until they have full enrollment. Some courses may have filled up prior to the start of the semester, but others don’t fill until a few days in.
Not everyone (at this point, at least) is taking an online course by choice, many are either waiting for a spot in an in-person class and eventually enroll in the online version as a Plan B when no in-person spots open up, or they choose the online course as a second choice when they discover after a few days that they don’t like their first choice and everything else in-person is full.
It would work differently in terms of start-up for an online summer course, those start on a much tighter timeline since the majority of the registration has happened a month or two prior.