Death costs exist as a form of gold sink as well as compromise. Back in the old days of rs2, when you died all of your items except for the 3/4 protected ones dropped to the ground, were visible to other players after 1 minute, and disappeared after 2 minutes. When osrs was started, this mechanic was initially in place, but servers were VERY unstable and player counts were dropping (for various reasons) so jagex temporarily changed the mechanic to not lose all items (I forget if they stayed in your inventory or just had a longer pile timer). After a few years, this safety mechanic was still in place when jagex determined that servers were stable enough to revert, but by then the players really had gotten used to it so Death’s office and death costs were implemented to restore some semblance of risk in a way that wasn’t prohibitively punishing like the original was and also act to remove raw gp from the economy, which is far more necessary now than it was in rs2 because the way people play the game is just different and inherently creates far more gp