This was possibly written for a specific sort of contest that people write webnovels for on certain websites. You have to use the theme to enter and all, so if you're not that crazy about isekai but want to get your work published you might end up writing one this way, where the isekai element is basically just there for show.I don't understand why this is an "isekai". This could easily be just a normal fantasy and have the exact same effect. The character goes to bed in one scene 8 years later in the other? The inbetween is what's great about rebirth isekai!