That's because with stalking, it's honestly kinda hard to prove that a: it is happening and b: it presents a real, tangible threat. Which matters, because the police can't actually do anything until those things are proven.

For example, if you both go to the same college, they can't just tell your classmate that he's not allowed to be in the same space as you because "he's making you feel unsafe". He's a student, he has a right to be there by default. They need some proof that he has actually done something wrong that puts you in danger. And the problem is, everything you describe him doing is difficult to prove. SA is hard to prove - that's why very few perps actually go to jail. Sure, he stole your camera - but how do you prove that to the police?
That's why they usually require something like a text message from his number, with an actual threat. Because that shows intent to cause harm, and it's something that can be easily verified.