Because they don't have the attribute 'light'. I think only two light weapons can be equipped for dual wielding, for instance daggers and short swords. Rapier don't count in it, which is a pity, cause I was looking forward to dual wield rapier + dagger.
At level 4, you can get another two weapon feat that will allow you to use non-Light weapons - so you can do the rapier + dagger combo
Yeah, but if short sword counted as light weapon, I was expecting rapier would too.
Rapier is not a light weapon.
https://roll20.net/compendium/dnd5e/Rapier#contentShort sword is a light weapon:
https://roll20.net/compendium/dnd5e/Shortsword#contentWhat I meant is that it's not historically and logically accurate.
Short Sword c. 1400
weight: 0.96 kg (2.1 lb)
blade length: 71.7 cm (28 in)
Rapier 1634-50
blade length: 38.7 in (98.3 cm)
weight: 2 lb 4 oz (1.02 kg)
But I understand the D&D rules want it to be otherwise. I guess by light, they mean small too.