Because
Sergeant
I'd second all of the above especially the XP thing. It feels odd that if as a player I am willing to take the time practicing combat skills that they don't get better at the same rate because sometimes I'm in a tournament and sometimes I'm not. I also don't see how it is particularly game breaking to allow a player to increase combat skills in this way as it is a single player game it's not like you are hurting any other player. Plus it gives you a good way to help companions level.+1 for the Warband Oldschool Arena it should have been the default tournament at Bannerlord release and then from there other types of competition could have been added with the participants own weapons and equipment or whatever.
Now that we are onto matters I would also like to lobby for full experience gain in Arenas because right now I think the player only gets 25% of xp for every action he does in the Arena: one handed weapons, running, shield blocking, bow, etc... and honestly I dont see any reason why we should not get 100% full xp instead if the combat actions are exactly the same than fighting in a battle... feels more like a punishment and lost work.