Because going for a night out and having a good time talking to someone doesn't necessarily translate to wanting that person to hit you up through social media the next day.
Especially if you're young. I've had nights out with my girls where we meet a group of guys who seem like a good time. Maybe one of our friends likes a guy around so we're wingwomaning, maybe they're good conversation.
All that doesn't necessarily mean I was interested in them. Sometimes it's just enjoying the night, going with the flow, especially if the intention that it was something more wasn't made clear...for allll the hours you were hanging out.
Dont take it personal and best of luck!