Because he doesn't assign as much importance and urgency to this connection that you do. If he did, well, this thread would not exist.
That's not to say he didn't like you, but only that he isn't operating from the same scarcity mindset that you are. What I mean is that you see this as your only shot at love and you have described your lack of success in dating generally - it is probably not the same for him, hence his willingness to let this one go. He knows this wasn't his only chance.
He also told you himself previously that he didn't have the right romantic feelings to continue dating you. You need to believe him. There is a difference between enjoying someone's company for the short term and having fun in the moment, and seeing true potential for something longer-term. The latter wasn't there for him. He was honest with you about that when he first ended this.
The fact that you remained open to seeing him in spite of knowing he felt that way is on you. No, he shouldn't have kept in touch knowing you liked him and wanted more. But it is up to you draw a line there and say no to casual meet-ups when the guy has not clearly indicated that he had a change of heart and wants to try dating again. It's a tough but important lesson to learn.
I hope you are not still communicating with him?