none of your posts explains why, having already earned money from the seats you built, you should get a full return of their value regardless of how much you earned.
Man just a very simply answer.
When you plan to increase your arena seats you also consider that it will be generate benefeits after 2 o 3 seasons... and noone expect to receive this benefeits the first season the build them.
so the BB's considered "Fair" to give some chances to get some of your money back. I see it as simple as it is.
Howl to the Moon, you won't regret it.