So, I'm making myself a Kobold Barbarian that is thematically addicted to cocaine, hence a reason to rage. But, I then have to stop and adjust my weapons accordingly, because small creatures have disadvantage with Heavy Weapon properties.

So, how come there isn't a feat for small creatures to use heavy weapons yet? I can't be the only one that has wanted a halfling to swing a Greataxe.

Balance perhaps.  Small races tend to get some great bonuses so the downside needs to come from somewhere.  

There is also a question of realism.  Body mass does equate to how much mass you can manipulate.  I understand that bringing up realism in a game where a 12 yo can make a fireball that kills twelve soldiers is a bit ...

Quote from OldElf86 >>

I understand that bringing up realism in a game where a 12 yo can make a fireball that kills twelve soldiers is a bit ...

I swear that was an accident!

Quote from Kaynadin >>

Balance perhaps.  Small races tend to get some great bonuses so the downside needs to come from somewhere.  

 Yeah, but its literally taking an Ability Score Improvement just to give them Greataxes. Maybe even Medium sized carrying capacity.

Mainly because this is 5th edition not 3.5 - Feats are not core to the game they are optional, variant rules intended to allow DMs to emulate 3.5 for their table of players.