Why would there be a deadline for 1Ls? A lot of people aren't even accepted yet. UM will take your FAFSA right up till the start of the semester.
Because this process is not geared towards helping us, the applicants. A lot of schools say to apply by the deadline, whether or not you've been accepted, and that applying after the deadline really does hurt your chances (slim as they were to begin with) for getting anything, assuming you even get in.
The most annoying part of that being that some schools use the Need Access and CSS, both of which cost money, and I don't get why they think it makes sense to make me pay to have this middleman service send paperwork about me and my finances to a school that won't give a damn because they rejected or waitlisted me.
Some schools, like Michigan, don't have deadlines. In general there doesn't seem to be a rule, but for a few schools the dates of choice seem to be tomorrow, as the OP realized, and 3/1.