For the same reasons rogues have been busted for the majority of wow pvp. Shamans have way way way too much utility which makes it such that if you give them any damage they become both broken in PVE and PVP. The class as it currently stands is why classic devs were terrified of giving any hybrid classes any power in their damage specs (spriest and ele resto having snuck through that bias).
Moveable totems that have party wide windfury, agility/strength buff, mana regen, fear removal, grounding totem/in combo with decoy totem grounding attacks, poison removal, disease removal, healing over time, snare/root immunity, (all with a redeployable 40 yard range mind you), spammable purge, access to heavy healing and ranged spell damaging abilities from melee dps spec (riptide/lavaburst), instant cast hard hitting spell procs from any spec (chain lightning and lava burst from power surge), 40% incombat movement speed (55% almost mount level speed with the pvp boots), interrupt dots and slows all on a 6 second cd with their shock spells.
It is just way way too much. If you give a class with that much utility any sort of damage they instantly become broken and the only way to fix it is to either rework their utility or make their damage useless (basically the wrath treatment rogues got).
In a 1v1 I personally have no problem with it because I can kite them into narnia and slowly drain their mana and kill them. Though wow is not a 1v1 game it is a group play game and when you have every derp hopping on the OP class train turing their alts into mains and theres 5+ shamans in every bg teamfight it just sours the game to a rather game breaking extent. There is 0 counter to them in group play.
Paladins don’t even eclipse half the group utility that shamans currently so you can count your odds based on how many band wagoner blue boys the enemy team has. There needs to be change because this class is the most broken thing I have ever witnessed in any iteration of wow and it is destroying sod pvp on a game breaking level.
If there is literally any hope for wow pvp something has to be done about this especially if pvp is moving away from burst damage which is the only thing that can remotely negate some of this gross amounts of utility.
edit: potential changes to be considered as if I am going to Reee about it I should at least be posing a solution:
Totemic Projection either having its cooldown lengthened to 45 seconds or have its usage limited to 1-2 times before having totems needing to be resummoned individually.
Remove the attack ground effect of Decoy Totem and make it incur a cooldown upon Tremor Totem and/or all other Earth Totems upon being summoned. Not a long cooldown more a short 10 second cooldown when Decoy Totem is summoned.
Make Lava Lash a much more required rune for enhance shamans over Lava Burst (a way to do this listed below) and fixing the scaling of Lava Burst.
Rework Maelstrom Weapon to proc off melee ability globals as opposed to melee attacks this way the proc doesn’t come immediately when getting in range of someone and strengthening the need for Lava Lash in Enhancement Talent Spec.
Nerfing and or moving Riptide from the wrist spot or making the mana regen from Rolling Thunder much more desirable/needed.
Strengthening the power though conversely need for Mana Tide Totem to strengthen the choice needed between utility and mana regen. There are plenty of ways to do this though the most effective I believe would be a rune next phase. (This last one is my own personal preference as I played a 60 ele/resto in Classic Era and I honestly hated having to drink 24/7 with Mana Tide Totem really not being remotely worth placing over Poison Cleansing Totem other than while I was drinking. Would be a fun dynamic if there was a choice at play here between a powerful dispell and powerful mana regen).