Mostly because it is hard to say that being a perma-enlarged fire giant or having inherent detect hidden isn't a massive massive boost in staying alive at the high ends of APdom. I'd take giant size (and the possibility of being enlarge-giant size) or detect hidden over felar bonuses any day of the week, but perhaps I'm missing something or overplaying the dangers of hiders to an AP at the top levels (meaning not just rank but once you start to snowball and need to essentially never die again).