So, this is how it used to be back in 3.5. You COULD sneak attack with a greatsword. That being said I understand why they made the change they did for 5e. Though come on let spears sneak attack!
Funny enough, I did find a spear in the game that gives you the effect of true strike when a you miss a creature in combat giving your next attack advantage. It very much feels like it's intended to be a rogue weapon but you have to wield it using strength because it's not finesse.
