Why do helicopter gunships suffer penalty from attacking over river?

[Stanley Fang]

I know helicopters are considered as land units in the game.
But it doesn't make sense to me that a hovering helicopter suffers penalty from attacking over river.

 

[jros83]

I know helicopters are considered as land units in the game.
But it doesn't make sense to me that a hovering helicopter suffers penalty from attacking over river.

It doesn't, but it's the same simplistic coding Civ has used forever; a unit type has the same fundamental coding regardless of how advanced it may be or what era you are in, such as the trope/meme "Spear Defeats Tank" because a Tank is "just" cavalry and spears are a hard counter to cavalry.