"More so because grad students receive grants that cover their tuition and some basic salary." That only tends to be true for PHD programs where the student is

"More so because grad students receive grants that cover their tuition and some basic salary." That only tends to be true for PHD programs where the student is expected to work on research that actually brings in grant money. That's not true for all grad programs. Some are not research-focused at all, and for those the student usually has to pay their own way or get other forms of financial aid (which not all students qualify for). Even if they do qualify for financial aid, they might not get any, if the limited amount that is available has already been given out to other qualified students.