Due to the recent Mob Arena Exploit found (Mob Arena [.Org] | Skyblock Forums), I thought "Why do a few people use this?".
I figured it out: They don't have a very good angle.
The spectator area is just a Ring around the arena, and I think that it would be better to make it covering the whole arena.
(Also, should probably fix the holes)

 

With the addition of the Invisible barrier blocks in 1.8, a Whole surrounding of the arena would be awesome for spectating. It'd be fun to get such a view.

 

Support! The angle of the mob arena is really really bad... you can't even move properly in that stupid ring -.-

 

They're already using the barrier blocks.

You can't exactly see what's in the middle.

 

Support, I enjoy spectatating the players at the mob areana, but its kinda hard to do so. There is barely enough room to move around and get a good view, if the view was better I believe more players would stuck around. Plus players in the areana would have more players cheering them on ^-^.

 

Support~
Sometimes there are a crap ton of players spectating and we just all crowd into one little area

 

I meant Ground level, or even As a full ceiling so we can stand above and watch below