Well, I am not a GM, but I can nevertheless tell you that this has to do with the greatly reduced player numbers on some Korean servers. While for example on Sieghardt (http://lineage2.plaync.com/gameinfo/olympiad/lastOlympiadInfo?serverId=50), which is population-wise comparable to Naia, there have been 19,544 Olympiad matches this month, Nevit (http://lineage2.plaync.com/gameinfo/olympiad/lastOlympiadInfo?serverId=42) had only 5,989 matches. This means that players on Nevit and the other low-population servers have to wait inordinately long until they find a sparring partner. Originally it was planned to solve the problem by switching to a Dimensional Olympiad where players from all servers would compete in the same arenas, but since NCsoft simply can't get a grip on multi-server technology (both the Dimensional Siege and the Dimensional Raid only started to be halfways functional after many weeks of fiddling), the developers decided to remove one arena instead, thus squeezing the participants into a smaller selection of places.
As to why this arena was removed and not for example the green "soccer field" which gives an advantage to ranged classes, that's something you would have to ask Nam Taek-rim, who was Chief Developer at the time :)