That's part of it, sure. But also the idea that you -can't- threaten someone 5ft away with a dagger. 'Cause it flattens the idea of reach pretty heavily.
In a fight between a guy armed with a knife and a guy armed with a sword, all other aspects being equal, guy with the sword is gonna kill the guy with a knife because of the reach advantage.
That's not to say it's gonna be a clean instantaneous death. Or that the guy with the knife can't also kill the guy with the sword by fighting through the pain and blood loss to get close in enough to take a stab or two.
But, y'know. Me holding a rapier and a foe holding a rondel, he's not getting close enough to me to stab without paying for it in advance. That's -why- rapiers kept getting longer and longer.
Now, now, let's not be hasty...
This is why most of my settings don't have gnomes in them, after all!