Relationships in general make people a bit nervous. It's about trust. Do I trust you enough to go there?
I am just hoping to meet someone who can discuss the world around them, is looking for more than just a date, and will cuddle on the couch and laugh with me. Will you be my partner in crime? If the answer is yes then message me and let's get lost together.
People could rationally decide that prolonged relationships take up too much time and effort and that they'd much rather do other kinds of things. But most people are afraid of rejection.