Merit awards serve a school's recruitment purpose. Schools use it to secure the best candidates whenever needed. Whether it's to get the students before April 30th or to get someone off the waitlist, as long as there is a need to use the funding, it's all fair game. Need awards are distributed to all students according to need in a consistent manner.
Here is the thing, WUSM's average debt is below $90k (which is a lot lower than schools that are famous for giving out tons of merit awards like Vandy and Penn), although we would not know how many merit awards are given out in a year, but judging from the low debt, there are probably quite a lot of them.