There are two answers to this.
First, it's often considered more enticing to the reader for things to occur in present tense rather than past tense. Part of the reason behind this is that things happening in present tense are easier to visualize in your head as happening right now, which lends itself to becoming engrossed in the story. I'm not sure how the psychology of this works in other languages, but for English-speakers it helps you feel like you're in the story. Another part is also the second big answer:
Voice. In English, a voice can be active, or passive. Active voice means that the subject of the sentence if performing the action (verb), such as:
Active: The dog bit the man.
Passive: The man was bitten by the dog.
Both mean the same thing, but it's generally considered best to use active voice (again, more engaging). Many people find it difficult to keep an active voice in the past tense, often because it can be difficult and doesn't generally sound as good.