Why Do So Many People Spend Real Money on In-Game Gold?

I don’t understand why people actively pay money just to avoid playing the game. If you buy 100 billion gold for €10 and use it to get all the gear, boss materials, runes, etc., then what’s the point of playing anymore? Why do people do this?

On top of that, all these gold buyers are driving equipment prices on Diablo.trade to absurd levels. Even service prices have become completely unreasonable—though, of course, they are affordable for those who buy gold.

What do you think about this? Have you ever bought in-game gold yourself? If so, why?