Two Weapon Fighting

Rules As Written

When you take the Attack action and attack with a light melee weapon that you’re holding in one hand, you can use a bonus action to attack with a different light melee weapon that you’re holding in the other hand (PHB 195).

House Rule

Attacking with a weapon in your offhand is part of the Attack action. It does not require a bonus action. You cannot take a bonus action to attack with the off hand weapon.

Rationalization/Reason for the Rule

Two weapon fighting, while cool, is much weaker compared to every other option. This carves a niche for the fighting style, giving users some flexibility & not requiring a feat investment to compete in damage. Great weapon fighting still significantly out damages two weapon fighting; this is intentional.