You've probably been refused based on 216(1)(b) - the officer doesn't think you'll leave Canada.
216 (1) Subject to subsections (2) and (3), an officer shall issue a study permit to a foreign national if, following an examination, it is established that the foreign national
(a) applied for it in accordance with this Part;
(b) will leave Canada by the end of the period authorized for their stay under Division 2 of Part 9;
(c) meets the requirements of this Part;
(d) meets the requirements of subsections 30(2) and (3), if they must submit to a medical examination under paragraph 16(2)(b) of the Act; and
(e) has been accepted to undertake a program of study at a designated learning institution.