Adademia Masters Admission Conundrum
Disclaimer: I do not work in admissions. My answer is simply based on my observation as a computer science student in the US.
When schools send admissions, they already have a yield rate (the percentage of accepted students taking the offer) in mind. If they have 30 spots for a program, they will most definitely send more than 30 offers. If the past yield rate has been around 1/3, they will send about 90 offers and expecting about 30 people to enroll. In general in the case of waitlist, they will only accept people if they have lower yield rate than past years.