Because it has already received 2 major os updates, what else do you want? According to Google's update policy every phone is supposed to receive two major OS updates and three years of security update. As On7 prime was launched with Android Nougat and it has received Oreo and pie updates as well, your device won't be getting any more updates.
see brother atleast next time do a bit of research Samsung makes phones that run on android and android is made by google so who gets to decide about the software well Google and it says 2 major os updates no more so there is nothing Samsung can do. one the bright side your phone is still going to be cool and you can continue to do whatever you do with your phone even without android 10
Almost all mid range phones are launched with the previous version of Android, only flagships are launched with the updated version. You can't do anything about that.
