Why is Casablanca so highly regarded? Curious cinephile

So I watched Casablanca some years back as it kept on being mentioned as amongst some of the greatest films of all time.

I watched it, and then I just wondered to myself....Why is this film so highly regarded? I felt bored and just could not connect with the story and didn't see the big deal.

I am really curious, what is it about the film that makes it so revered? Is it when it came out? Had there never been a film that told the story in the way it did?

Curious...