A CS masters is the last kind of degree Stanford would give good financial aid for. For a bachelors degree, you can get need based aid, and for a Ph.D, it's customary that you're pretty well subsidized, but masters programs are where they get you. I'm not sure why.
PhD students are essentially junior employees of the university. They're either teaching or conducting research, so they're getting paid (largely in the form of free tuition).
Masters students are customers buying an extra year or two of education.
A substantial proportion are also foreign students from wealthy families looking to get their students a prestigious U.S. degree. Such families are quite willing/able to pay, so there's no great incentive for Stanford to subsidize them.
