* You already know the story. This is probably the biggest reason why a movie can feel less exciting the second time around. When you know what's going to happen, there's less suspense and surprise.
* You're more critical the second time. The first time you watch a movie, you're more likely to be swept up in the story and overlook any flaws. But the second time around, you may be more critical of the acting, the directing, the writing, etc.
* You've changed since you first saw the movie. Your tastes and interests may have changed since you first saw the movie. What you found exciting or funny the first time may not seem as appealing the second time.
Of course, there are also some movies that get better the second time you watch them. These are often movies that are complex and have a lot of depth. The more you watch them, the more you appreciate the nuances and subtleties.
Ultimately, whether or not a movie is better the second time you watch it is a matter of personal opinion. There are pros and cons to both watching a movie for the first time and watching it again. If you're not sure whether or not you'll enjoy a movie the second time, you can always rent or stream it before you buy it.