Because they are only guards, like those in Malls/Supermarkets/etc.
They are not Heroes of Azeroth who killed Ragnaros/Deathwing/Lich King/etc, they are just guards.
Some classes counter other classes, like Paladins could be a problem for a Shaman, but they a walk in a park for a Mage. You can’t win them all, not by just yourself for sure, so if you want to - get help/friends/guildies… it’s like solving a Player vs Player problem with actual Players and not NPCs.
P.S.: Want to join WPvP guild / community, or tell others about yours - go here and DO IT