There are many reasons that college students have these eating habits.that后面是什么从句

that college students have these eating habits这是个定语从句,修饰先行词reasons我一度认为是个同位语，能给我详细解释一下吗？以此题为例。如果是同位语，那去掉many reasons的话，句子应该是成立的，而本句中“There are college students have these eating habits.”是不成立的。