Because you have 28% haste, for starters.
WHM is very attack and fSTR starved, so incorporating those things is a good idea. You're also going to be mostly meleeing weak things, so accuracy is usually not a big deal. Evergreen Earring is pretty terrible.
Probably a fair assessment against the Earring, Ghillie is probably better, although it would cut into Subtle Blow (but only a very, very small amount).
I'm aware it goes a little too far with haste. The issue is that I couldn't find something I considered a good tradeoff against it - for example, dropping more then 2 sTP would drop it down a hit, and using a Brutal will gimp the Kraken Club.
Dropping Savateur's Gaiters in order to drop the Haste down for example, would drop you below the Subtle Blow cap. Muddle Pumps were something I considered since they add +5 STR while keeping as much accuracy, but the Subtle Blow seemed better then +5 STR.
Furthermore, most White Mage sets I've traditionally seen have been geared towards getting TP faster so you can spam Hexa/Realmrazer faster, since that greatly outpaces white damage generally - I'll need a bit of math to be convinced of any build that raises hit requirements to do more damage during auto-attack rounds, although trading accuracy/attack is something easier to understand without busting out the numbers.
Also no, Savateur's gaiters don't win. Kthonios/Shedir/Rubeus/Ninurta/Iuvenalis/Blessed+1 is the optimal haste combination for anything a WHM will be hitting.
That's 1% short on Haste unless you can pull the exact Haste values to actually cap out Haste.
Store TP actually matters a small amount, since it will be reducing the amount of hits needed, and adding double attack gear nerfs your Kraken Club, so a White Tathlum would be absolutely required to make a Kthonios set worthwhile. Additionally, I feel Iuvenalis is the wrong choice, +7 STR isn't going to be worth the 1% extra Haste.
The argument I really see is the +14 attack during auto-attack rounds against +8 accuracy and being able to cap Subtle Blow. Additionally, since the set I originally set forward has the added bonus of having a bit of haste leeway, you could use the Iuvenalis in that set instead, adding +7 STR, which shallows the gap between the two sets if both strive to cap their haste like any good set will do.
Kthonios/Shedir/Blessed+1/Rubeus/Ninurta/Blessed+1/White Tathlum probably wins out over Zelus/Shedir/Iuvenalis/Rubeus/Goading/Savateur's/White Tathlum in terms of damage while keeping the same hit count, since it is about twice the attack for half the accuracy and being able to cap Subtle Blow. I think the stat difference is still small enough however to make it a somewhat hard choice between the two.