It's hard when people aren't direct about their feelings. It makes it difficult to move forward because we don't want to make assumptions. These types of people try to "give a hint", to express what they are feeling without actually having to tell you.
Basically "mind reading expectation" that everyone interprets the same behavior as meaning the same thing.
I've had plenty of people tell me they weren't interested and move on. I've told people that, too.
I think there are some people who are afraid to be authentic and would rather avoid the risk of conflict. It's an avoidance behavior that is somewhat encouraged by our culture.