Why is it forbidden to take chests on the battlefield?

In principle, Amaranth has already answered this. I just want to expand on the answer a bit (I pointed this out to VDV_forever even before the tournament started).
The thing is, in a battle with a specific neutral creature, you can time it so that the battlefield will be different, and accordingly, 1 or 2 chests may appear on it, and they may randomly contain: either gold, or runes, or a scroll with a spell, and even an artifact. So, to ensure that everyone is on equal footing, the decision was made that chests on the battlefield should not be taken. (because, a cool scroll with a spell that cannot be bought in Darien might appear...).
And pay attention (if anyone hasn't noticed in the rules) - it is forbidden to flee from the battlefield;).