Everyone just wanted to live and be happy. We desire what we do because we believe it would get us happiness. As such, in a fucked-up world right now, most people desire to escape. This gave birth and steam to Isekai.
In most Isekai, people had a cheat and were allowed to be their own superheroes. Alone they would impact a world. Alone they would gain love and respect and happiness. As Isekai was primarily a genre of fiction it naturally had an ending.
And as most of these endings were happy. Because who the fuck would want to read a tale where everything ended in tragedy. Not unless your goal was to piss everyone off. As Anime and Manga were in the end business most were given happy endings just for the readers satisfaction.