Why is it that every single defensive item is not gold efficient in terms of raw stats, whereas 95% of offensive items are more than gold efficient in terms of stats without adding in the passive?
And why, on average, do defensive items cost more?
Rito pls, I would like to live longer than 5 seconds when only the ADC is attacking me
I have a solution!
We can nerf the gold-to-effect ratio of cloth armor, null-magic mantle, and ruby crystal (which are used as base markers for gold efficiency calculation) so that all defensive items that build out of these basic components will end up with a "higher" gold efficiency!
/end troll post
Why is it that every single defensive item is not gold efficient in terms of raw stats, whereas 95% of offensive items are more than gold efficient in terms of stats without adding in the passive?
Every item is different. It's difficult to generalize without being at least somewhat inaccurate. With that said, in general, the cost inefficient defensive items have really strong uniques 
while the cost efficient offensive items are weaker in that regard
This topic would be more productive if you were to discuss specific items, rather than trying to paint with a broad brush.
And why, on average, do defensive items cost more?
I don't think this is true. The top 5 most expensive items in the game are offensive items
.
Keep it going, you say? Okay, here's everything that costs more than 3k:
Looks to me like offensive items have near monopoly status up here. Zhonya's is amazing for both offense and defense, leaving Mallet as the only item on the list that is a defensive buy, and basically it's unused today by serious players.
Rito pls, I would like to live longer than 5 seconds when only the ADC is attacking me
This won't happen in the late game. Offense has to outscale defense or games don't end.
Defensive items are useless in this game, the only one who win is the one that burst the enamy first. Just thing to l.w or void staff, an item that counter many difensive items....
Not only are offensive items vastly more cost effective than defensive ones, building for optimum effective hit points (EHP) is nearly impossible. Against someone with %Pen masteries and Void/Whisper you need about 2400 HP for every 100 resist otherwise you're wasting stats.
How easy is it to get 200 armor (which is getting negated by Whisper)?
How easy is it to get 4800 HP (which is getting shredded by BotRK)?
