Present tense writing paves the way
While writing in the present tense is becoming more and more common, it is still a bit of a shock when you open a book and the first thing you read is; the girl writes her journal, or; the boy walks down the street.
James Joyce wrote the first book entirely in the present tense, his 1918 novel Ulysses. Since then, many more books have been written in the present tense, and many more will be written in the years to come.
However, use of the present tense dates back all the way to when Charles Dickens was writing his novels. His novel Bleak House is split between past and present tense. This was a very new idea at the time, although it grew in popularity, especially when the Bronte sisters used it in one of their books.
Now, most young adult books are written in the present tense, and there is a very specific reason for this. Most readers of young adult (YA) fiction do not hold as much reverence for the past as most adult readers. Adults want to read about the past, they find it to be interesting and intriguing. Children do not. They are entirely focussed on the present, and what is happening to them right now. For these reasons, most YA novels are written in the present tense. This keeps younger readers more entertained, and it helps most young people develop a taste for reading.
Present tense and past tense both have their merits. Past tense is much easier to write in, and it gives most readers a sense of comfort, as most of the books that people have read are written in the past tense, but books written in the present tense are new and fresh. They give the reader the feeling of being inside the story. It gives the reader the sense that they are not just reading the book, they are inside the book.
It also helps the reader feel a connection to the main character of the story. Having the book be written in first person makes the reader feel a sense of immediacy. It makes them feel closer to the story, and the main character because they are witnessing important events and transformations as they happen, instead of simply hearing about them from a later point in time.
Another reason present tense writing is often used in young adult novels is because it is easier to write about the future, or an undetermined point in time, while writing in the present tense.
Many young adult dystopian books take place in the future. It makes more sense to write about events that have not yet happened in a present tense voice, rather than a past tense one. The Hunger Games is a very popular young adult dystopian book and it takes place in the present tense. Many young adult fantasy or realistic fiction books also take place in an undetermined time. For fantasy books, it is because the fictitious world does not coincide with our world, and therefore their timeline does not match up with ours. In realistic fiction books, such as the very popular book Screeenshot, it is often because the author wants the story to be timeless. It could have taken place fifty years in the past, fifty years in the future, or fifty minutes ago in the town where you live. Because of this, it is easier to use a present tense voice.
Present tense writing, while it is fairly new, is not going out of style any time soon.