When M'Kathu commanded the people of the Border Tribe to attack Black Panther, how exactly were they trying to subdue him? At one point Black Panther was thrown like a quarter mile by a battle rhino and was on the ground being hacked at from all sides by the Border Tribe people... but it wasn't doing anything to him! He just lay there looking at Nakiya fight Killmonger for a couple seconds and then sat up and blasted everyone away. The Border Tribe people had to have known that it was futile to use their hand weapons... but then why is that all they did when they surrounded him?
The fancy Vibranium nano-suit was brand new. T'Challa appears surprised and impressed at its kinetic storage and blast abilities.
It is reasonable to assume that the warriors were not aware of these abilities, and expected massive sharp trauma to actually do something like it usually would.
The frenzy of battle accounts for them not realising that something odd was happening and changing their tactics.