This sound comes from the musical identity of Halo, the flagship sci fi video game series that began in 2001. The Halo theme became famous for its instantly recognizable, emotional melody and has appeared in many fan edits, gaming compilations and nostalgia posts for years. Short piano focused cuts are especially popular because they keep the recognizable feel while fitting quick videos. It still gets reused whenever creators want to signal heroism, loss, scale or old school gaming memories in just a few seconds.