Ench Shamy PoD Question / Talents

[healticket]

I got a question about the talents that almost all Ench Shamys are running at 39 with PoD.

Shaman Classic Talent Calculator - World of Warcraft (wowhead.com)

Why do they go with 4/5 Flurry instead of 5/5? What is the reason behind it?
Thanks!